MRO Control Zero H7 OEM USART6 support

[benjinne]

Describe problem solved by the proposed feature

Hi, I am trying to use the SPI6/USART6 port on the control zero to have access to the full uart for CRSF telemetry and bind capability, however I can't get it working.

I changed the USART6 definitions in board.h to my best guess of the pins

#define GPIO_USART6_TX GPIO_USART6_TX_2 /* PG14 /
#define GPIO_USART6_RX GPIO_USART6_RX_2 / PG9 */

running crsf_rc start -d /dev/ttyS3 should work when connected to a CRSF receiver and connected to the SPI6/USART6 port

Describe your preferred solution

Add definitions to the board config to enable USART6 even if it's commented out. That way it's easy to enable if needed on custom firmware

Describe possible alternatives

none

Additional context

No response