- Adds core option to allow battery saves using the libretro api
(retro_get_memory_data/size)
- Initial save size set at 128KB and actual size is automatically
determined internally by gba.
- This will always assume that a save file is supported since save
size or type cannot be determined until gba tries to write to backup memory.
- A 128KB block of memory is used as buffer, similar method to VBA
Next/Beetle GBA workarounds.
Fix https://github.com/libretro/gpsp/issues/72
