Reduce ROM size of USB_EPStartXfer

[KozhinovAlexander]

This issue were observed within zephyr rtos project using stm32g4, USB stack from zephyr rtos and stm32g4 HAL drivers.

Is your feature request related to a problem? Please describe.
USB_EPStartXfer for stm32g4 has 1440 KiBi text section, which is huge in my opinion.

Describe the solution you'd like
The size of USB_EPStartXfer shall be reduced or the reason for such text section size shall be mentioned.

Describe alternatives you've considered
none

Additional context
To reproduce the behaviour any USB sample for stm32g4 could be taken. Afterwards execute ninja -C build rom_report > rom_report.log.

In my case I am getting following values:

ninja: Entering directory `app/build'
[0/1] cd $HOME/Documents/dev/cannectivity/app/build &&  $HOME/Documents/dev/zephyrproject/.zephyr_venv/bin/python3  $HOME/Documents/dev/zephyrproject/zephyr/scripts/footprint/size_report -k  $HOME/Documents/dev/cannectivity/app/build/zephyr/zephyr.elf -z $HOME/Documents/dev/zephyrproject/zephyr -o  $HOME/Documents/dev/cannectivity/app/build --workspace= $HOME/Documents/dev/zephyrproject -d 99 rom
WARN: Symbol 'z_tls_current' section '' is not in RAM or ROM.
Path                                                                                             Size       %  Address    Section    
==========================================================================================================================================
Root                                                                                            61146 100.00%  - 
├── (hidden)                                                                                     8088  13.23%  - 
├── (no paths)                                                                                  53056  86.77%  - 
│   ├── AHBPrescTable                                                                              16   0.03%  0x0800defd rodata
│   ├── APBPrescTable                                                                               8   0.01%  0x0800def5 rodata
│   ├── CSWTCH.490                                                                                 20   0.03%  0x0800bde8 rodata
│   ├── HAL_PCD_DataInStageCallback.constprop.0                                                    36   0.06%  0x0800b721 text
│   ├── HAL_PCD_DataOutStageCallback.constprop.0                                                   56   0.09%  0x08007579 text
│   ├── HAL_PCD_SuspendCallback.constprop.0                                                        20   0.03%  0x080075b1 text
│   ├── LL_RCC_HSI_IsReady                                                                         16   0.03%  0x08005ee5 text
│   ├── LL_SetFlashLatency                                                                        220   0.36%  0x08006031 text
│   ├── LL_TIM_ClearFlag_CC1                                                                        8   0.01%  0x0800a805 text
│   ├── LL_TIM_ClearFlag_CC2                                                                        8   0.01%  0x0800a80d text
│   ├── LL_TIM_ClearFlag_CC3                                                                        8   0.01%  0x0800a815 text
│   ├── LL_TIM_ClearFlag_CC4                                                                        8   0.01%  0x0800a81d text
│   ├── LL_TIM_DisableIT_CC1                                                                       10   0.02%  0x0800a82f text
│   ├── LL_TIM_DisableIT_CC2                                                                       10   0.02%  0x0800a843 text
│   ├── LL_TIM_DisableIT_CC3                                                                       10   0.02%  0x0800a857 text
│   ├── LL_TIM_DisableIT_CC4                                                                       10   0.02%  0x0800a86b text
│   ├── LL_TIM_EnableIT_CC1                                                                        10   0.02%  0x0800a825 text
│   ├── LL_TIM_EnableIT_CC2                                                                        10   0.02%  0x0800a839 text
│   ├── LL_TIM_EnableIT_CC3                                                                        10   0.02%  0x0800a84d text
│   ├── LL_TIM_EnableIT_CC4                                                                        10   0.02%  0x0800a861 text
│   ├── LL_TIM_OC_GetCompareCH1                                                                     4   0.01%  0x0800a7f5 text
│   ├── LL_TIM_OC_GetCompareCH2                                                                     4   0.01%  0x0800a7f9 text
│   ├── LL_TIM_OC_GetCompareCH3                                                                     4   0.01%  0x0800a7fd text
│   ├── LL_TIM_OC_GetCompareCH4                                                                     4   0.01%  0x0800a801 text
│   ├── LL_TIM_OC_SetCompareCH1                                                                     4   0.01%  0x0800a7e5 text
│   ├── LL_TIM_OC_SetCompareCH2                                                                     4   0.01%  0x0800a7e9 text
│   ├── LL_TIM_OC_SetCompareCH3                                                                     4   0.01%  0x0800a7ed text
│   ├── LL_TIM_OC_SetCompareCH4                                                                     4   0.01%  0x0800a7f1 text
│   ├── SEGGER_RTT_WriteSkipNoLock.constprop.0                                                    112   0.18%  0x0800760d text
│   ├── SystemCoreClock                                                                             4   0.01%  0x20000f1c datas
│   ├── USB_ActivateEndpoint                                                                      776   1.27%  0x08006cb5 text
│   ├── USB_EPStartXfer                                                                          1440   2.36%  0x0800ae4d text

especially:

│   ├── USB_EPStartXfer                                                                          1440   2.36%  0x0800ae4d text