Fix Viki SDCARDDETECT for MakerGear M2

Fixed #ifdef and added comments for connection of VIKI.  This restores
sd card detection and button functionality.

Differing from MakerGear's instructions:
Yellow wire from EXT2 pin 15 should land on EXT2 pin 14.  Black wire
from EXT2 pin 13 should land on EXT2 pin 20.