Merge branch 'ax215' of github.com:xobs/ax211-code into ax215

Conflicts:
	progs/debugger.asm
	src/ax215/execute.c
debugger: Validate communication on startup

We verify that communication works by using the CMD_HELLO opcode to
have the card echo a known-good string back to us.
debugger: Get fully working on AX215

This is the last of the patches to get the basic debugger working
on the AX215.  SFR and IRAM modification works, disassembly works,
and most things are generally working.

NAND commands don't yet work.