Libretro: Redo key handling, support bitmasks
Libretro: Redo key handling, support bitmasks

libretro/mgba,mgba-emu/mgba,libretro/mgba,Iniquitatis/mgba,Iniquitatis/mgba,Iniquitatis/mgba,mgba-emu/mgba,Iniquitatis/mgba,mgba-emu/mgba,mgba-emu/mgba,libretro/mgba,libretro/mgba,libretro/mgba