Provide option to enable SGB+GBC support

[fekir]

Since mgba-0.10.0, mgba supports the "Super Game Boy Color" (see https://mgba.io/2022/10/11/mgba-0.10.0/#super-game-boy-color)

Some games take advantage of this feature, for example

• https://github.com/ShockSlayer/ccdocs/blob/master/docs/changelogs/2_4_0_Changelog.md#2_4_0_SGB_Border
• https://www.romhacking.net/hacks/4672/
• https://www.romhacking.net/hacks/7724/

but there is no option in retroarch mgba code for enabling "Super Game Boy Color", and with autodetect turned on, no dynamic borders are shown.

[hizzlekizzle]

I took a stab at this, hoping it would just be a matter of adding the SCGB model here (https://github.com/libretro/mgba/blob/master/src/platform/libretro/libretro.c#L1183), but there's apparently more to it.

[endrift]

I actually already did this upstream, but given the status of #291 being in seeming limbo, I haven't really tried to get things merged back downstream in a while.

[hizzlekizzle]

ah, yeah, I forgot about that one. I'll follow up with ryunam to see if they have some time to try and get the ball over the line (or whatever sportsball metaphor is appropriate here)

[fekir]

Hello, I see that #291 has been marked as closed because of #304

There is now an option for enabling SGB+GBC support, thus this issue can be closed (unless there is some follow-up work to do and one wants to use this for tracking progress)

Would it, for example, make sense to accept sgbc as file extension for enabling SGB+GBC by default? (and sgb for enabling SGB by default?)
Currently the supported extensions are gb,gbc,gba