AP_HAL: clean up UART driver storage/access and legacy ordering #34153

Job	Run time
build (stm32f7, chibios, 10)	15m 10s
build (stm32h7, chibios, 10)	11m 56s
build (fmuv2-plane, chibios, 10)	5m 30s
build (periph-build, chibios, 10)	17m 45s
build (iofirmware, chibios, 10)	2m 25s
build (CubeOrange-bootloader, chibios, 10)	1m 9s
build (fmuv3-bootloader, chibios, 10)	59s
build (revo-bootloader, chibios, 10)	1m 3s
build (stm32h7-debug, chibios, 10)	7m 7s
build (fmuv3, chibios, 10)	12m 48s
build (revo-mini, chibios, 10)	10m 2s
build (MatekF405-Wing, chibios, 10)	10m 58s
build (CubeOrange-ODID, chibios, 10)	8m 32s
build (CubeRedPrimary-bootloader, chibios, 10)	1m 32s
build (configure-all, chibios, 10)	8m 42s
build (build-options-defaults-test, chibios, 10)	20m 12s
build (signing, chibios, 10)	9m 5s
	2h 24m 55s

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