Added DroneCAN support

[tridge]

This adds DroneCAN support to AM32 and enables it on the VIMDRONES_L431 ESC

Features working:

• motors spinning
• parameter save/load/erase
• debug text messages
• ESC status messages working
• firmware update over DroneCAN
• ArmingStatus working
• node restart
• bi-directional support
• firmware signature checking in CAN bootloader: added DroneCAN bootloader support AM32-bootloader#21
• need to switch L431 to using HSE crystal instead of HSI

Remaining issues:

• cell count should be a separate parameter, detection can be unreliable

[ianrmurphy]

@tridge now we have a bootloader for the B-G431B-ESC1, it should be possible to rebase this support onto that ESC. Can you review that task? If not I will be able to take a look later in the week. Note, I would need to setup a DroneCAN environment first.I have a suitable FC and I think I have an SLCAN device somewhere, need to dig it out and give it a try.
Otherwise, is there a DBC file available for DroneCAN? If so I have other CAN tools ready to go.

[ianrmurphy]

Also, I have tonight run a motor using the ST MC Workbench FOC code, not AM32. Would be possible I think to extend that for DroneCAN support without much work.

[Quick-Flash]

What does this have to do with DroneCAN? This shouldn't live here, if anything it should be something that can be optionally used by any ESC protocol, this just doesn't make sense.