Implement crash dump

[kanflo]

Getting "timeout talking to device" is quite a drag when we could have gotten something more verbose such as "sorry, but your DPS crashed at 0x12345678 and rebooted" with some registers.

When the app crashes it should write a crash dump into the bootcom area (which need to increase). Upon restart, the app should make this dump available to dpsctl. Here is a copy-and-pasteable fault handler: https://github.com/kanflo/aaduino-zero/blob/master/common/faulthandler.c