UNIMAP: Undefined layers in firmware

[tmk]

when you don't define unused layers in keymap file, flash memory space for the undefined layers is filled with 0xFFFF(on AVR at least) and the the code is not valid for unimap action. It would be better that the undefined space is filled with TRANS(or NO) action.

TMK keymap editor fill the undefined space with 0x0001(TRANS) when its firmware is downloaded. This is not a problem here.

Solutions:

1. Change code to reognized 0xFFFF as TRANS(or NO).
2. Change linker script to fill with TRANS(or NO)