chibios_hwdef.py: allow re-use of bootloader from other boards

[peterbarker]

This should be useful for people wanting to make OEM setups but don't want to re-build (or copy...) the bootloader.

env added HAS_EXTERNAL_FLASH_SECTIONS=0
env added CHIBIOS_BUILD_FLAGS=USE_FATFS=yes CHIBIOS_STARTUP_MK=os/common/startup/ARMCMx/compilers/GCC/mk/startup_stm32h7xx.mk CHIBIOS_PLATFORM_MK=os/hal/ports/STM32/STM32H7xx/platform.mk MCU=cortex-m7 ENV_UDEFS=-DCHPRINTF_USE_FLOAT=1
Padded 16 bytes for bootloader.bin to 38816
Embedding file bootloader.bin:/home/pbarker/rc/ardupilot/Tools/bootloaders/CubeOrange_bl.bin
Embedding file defaults.parm:/home/pbarker/rc/ardupilot/build/e0-CubeOrange/processed_defaults.parm
Embedding file hwdef.dat:/home/pbarker/rc/ardupilot/build/e0-CubeOrange/hw.dat

Note it getting the bootloader from CubeOrange, not e0-CubeOrange That's because of this hwdef:

diff --git a/libraries/AP_HAL_ChibiOS/hwdef/e0-CubeOrange/hwdef.dat b/libraries/
AP_HAL_ChibiOS/hwdef/e0-CubeOrange/hwdef.dat
new file mode 100644
index 00000000000..34acb794376
--- /dev/null
+++ b/libraries/AP_HAL_ChibiOS/hwdef/e0-CubeOrange/hwdef.dat
@@ -0,0 +1,3 @@
+include ../CubeOrange/hwdef.dat
+
+USE_BOOTLOADER_FROM_BOARD CubeOrange

[andyp1per]

LGTM