AP_EFI/AP_PiccoloCAN: Add Currawong ECU support

[reilly-callaway]

• Reads telemetry data over CAN and pass to existing AP_EFI_Backend.
• Configurable to send throttle commands over CAN to a single ECU.

Example with Currawong ECU connected to CubeOrange over CAN. Shows EFI mavlink status in Mission Planner (matching data in Currawong's internal tool) with throttle set by Ardupilot:

[reilly-callaway]

Rebased on top of master and to clean up commit history, happy to squash it down more if you'd like.

[SchrodingersGat]

@hendjoshsr71 any further requirements for review on this?

[reilly-callaway]

@tridge @peterbarker Any updates on having this approved?

[tridge]

@reilly-callaway needs a rebase as conflicted, then ping me to merge this

[reilly-callaway]

@tridge Rebased and all tests passing. Should be good to merge.

[peterbarker]

Merged, thanks!