use the flag set by the GAME/CONS/COMP/SYST macro to parse additional optional ini files
GAME = GAME_TYPE_ARCADE -> arcade.ini
CONS = GAME_TYPE_CONSOLE -> console.ini
COMP = GAME_TYPE_COMPUTER -> computer.ini
SYST = GAME_TYPE_OTHER -> othersys.ini

I've had a few requests to do this and it seems simple enough to leverage the flags we already have.