Add support for ModalAI FC1 target

[modaltb]

Describe problem solved by this pull request
This PR is to add support for the ModalAI Flight Core 1 board. This has some commonality with the v5x hardware but is a derivative with designs to mate with the VOXL companion computer. The fmu_v5x board support was used as the starting point.

The bootloader update for this board has a PR here:
PX4/PX4-Bootloader#155

Describe your solution
NA

Describe possible alternatives
NA

Test data / coverage
Flight testing has been ongoing for the last months with positive results. Please push back and let me know if more is needed! :)

Additional context
I can ship hardware to anyone if needed for testing, just let me know!

[dagar]

Can you add the build to Jenkins? https://github.com/PX4/Firmware/blob/cefa7ec5dc55ea03c0518670c3622043a535676c/.ci/Jenkinsfile-compile#L38

[modaltb]

Not sure if the Jenkins job picked up the change with the added target, it's not appearing in the "Compile All Boards" step. I can re-submit a PR if needed to 'flush' the change if that's needed.

[hamishwillee]

When you're in production you might want to document the board. Typically that is done in 2 places:

• board docs: https://docs.px4.io/master/en/flight_controller/
• quick start: https://docs.px4.io/master/en/assembly/quick_start_cuav_v5_plus.html

[modaltb]

@hamishwillee thanks for the heads up, I created a task on our end to get this in place before production release.