GCS_MAVLink: Add support for parity to Serial passthrough #39007

Job	Run time
build (stm32f7, chibios, 10)	14m 13s
build (stm32h7, chibios, 10)	12m 28s
build (fmuv2-plane, chibios, 10)	4m 11s
build (periph-build, chibios, 10)	12m 48s
build (iofirmware, chibios, 10)	2m 31s
build (CubeOrange-bootloader, chibios, 10)	1m 5s
build (fmuv3-bootloader, chibios, 10)	1m 5s
build (revo-bootloader, chibios, 10)	1m 3s
build (stm32h7-debug, chibios, 10)	7m 38s
build (fmuv3, chibios, 10)	13m 18s
build (revo-mini, chibios, 10)	10m 27s
build (MatekF405-Wing, chibios, 10)	10m 45s
build (CubeOrange-ODID, chibios, 10)	8m 26s
build (CubeRedPrimary-bootloader, chibios, 10)	1m 17s
build (configure-all, chibios, 10)	10m 14s
build (build-options-defaults-test, chibios, 10)	26m 23s
build (signing, chibios, 10)	9m 9s
build (CubeOrange-PPP, chibios, 10)	6m 42s
build (SOHW, chibios, 10)	12m 44s
build (Pixhawk6X-PPPGW, chibios, 10)	2m 36s
	2h 49m 3s

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