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)