Implement setting to force flash size

[tau-]

Adds libretro setting to toggle between automatic detection and fixed sizes for the cartidge flash. Allows for selection of "auto", "64kb", and "128kb" options. This allows for compatibility with roms which need a specific amount of memory but do not appear in the list of known overrides.

[saulfabregwiivc]

Very nice :)

[davidgfnet]

I will check this out, please do not merge it just yet.
Also, I plan to update the gba_overrides file using some repo I created, to have a proper completi-sh list of games and their config.

[davidgfnet]

Hey, mind telling me which games do you think this would be useful for?
Also would be better to have a setting to force a storage type and size. As of today only these exist:
None, SRAM (32KB), EEPROM (512bytes / 8KB), FLASH (64 / 128KB). It might be just easier to have an option to select among those ones.

[tau-]

I originally implemented this to support various rom hacks which are not listed in the overrides list (as they may have modified headers) but require 128kb of cartridge flash to function. Generally I think having a way to manually select this option would be great for allowing combability with homebrew. This could be reworked as you described to allow selecting from a small list of known cartridge configurations, but I did not look carefully into the SRAM and EEPROM emulation, so I will leave this open for now if you have additional feedback.