3DS: Minor fixes for GPU issues, detect usable cores better
3DS: Minor fixes for GPU issues, detect usable cores better

libretro/mgba,mgba-emu/mgba,Anty-Lemon/mgba,libretro/mgba,Iniquitatis/mgba,Anty-Lemon/mgba,libretro/mgba,Anty-Lemon/mgba,mgba-emu/mgba,Iniquitatis/mgba,Iniquitatis/mgba,libretro/mgba,Anty-Lemon/mgba,mgba-emu/mgba,mgba-emu/mgba,Iniquitatis/mgba,libretro/mgba