ax215: main: Use enum for program mode

Instead of hardcoding mode numbers, use an enum.  This increases readability.
ax215: fuzz: Ensure SFR is actually an SFR, not RAM

OR in 0x80 with the SFR values, to ensure we're writing to the SFR region,
and not just to RAM.
A5TestBoot: Add script for AX215

This is the AX215 version of the testboot script.  In source form.