This adds support for the full-sized FMUv4PRO design and the FMUv5 STM32F7 based generation.

* Fix minor spelling error

* Added support for the AUAV x2.1 Flight Controller
    also removed a duplicate entry for MindPX
    from src/comm/USBBoardInfo.json

Adds entries required to correctly identify, download and flash PX4
firmware to the AUAV X2.1 Flight Controller

* Update USBBoardInfo.json

Removed un-needed fallback entries. This has been tested!

* Add support for another board

* Added a 2nd custom board

Verify was failing due to incorrect READ_MULTI max size

Usability plus, new features:
- 3DR Radio support
- APM Stack support