UAVCAN sensor node (and px4_fmu-v4_cannode example)

[dagar]

This pull request resurrects the existing uavcannode module and updates it to publish baro, mag, and gps data on CAN (if that data is available on uORB). I've also created an fmu-v4 config for testing (px4_fmu-v4_cannode).

@igalloway @dk7xe this is the higher level plumbing for a CAN sensor node. We can easily enable it on the rddrone-uavcan146 once the CAN driver is settled.

nsh> uavcannode start
INFO  [uavcannode] Node ID 120, bitrate 1000000
INFO  [uavcannode] SW version vcs_commit: 0x7fffffff

nsh> uavcannode status
Pool allocator status:
        Capacity hard/soft: 500/250 blocks
        Reserved:  5 blocks
        Allocated: 4 blocks

UAVCAN node status:
        Internal failures: 0
        Transfer errors:   0
        RX transfers:      0
        TX transfers:      41998

CAN1 status:
        HW errors: 0
        IO errors: 0
        RX frames: 0
        TX frames: 41998

uavcannode: cycle time: 108497 events, 3446228us elapsed, 31.76us avg, min 17us max 377us 32.127us rms
uavcannode: cycle interval: 108497 events, 2413.46us avg, min 32us max 10037us 2813.759us rms

[dagar]

Future todo items:

• UAVCAN node as an airframe selection
• parameters (UAVCAN <=> PX4)
• estimator support?
• servo support?

[dk7xe]

Great! Thank you for starting on this. @LowOrbitIonCannon, @jarivanewijk , @PetervdPerk-NXP fyi