Fix AVRISP-MKII clone project's TPI Chip Erase command processing - ensure...

Fix AVRISP-MKII clone project's TPI Chip Erase command processing - ensure erase location is the high byte in the given address space, check NVMBUSY for completion rather than the NVM Bus Enable bit.

Change If-Else chains over to switch statements in XPROGProtocol.c for clarity.