[bsnes] SA-1 support almost complete

Added character conversion DMA mode 1, which fixes level up text in Mario RPG, making it fully playable now with no known issues. Fixed character conversion DMA mode 2, which fixes SD Gundam G Next's graphics. Fixed variable bit-length reading, which fixes Jumpin' Derby's graphics. Improved the SA-1 chip detection code, allowing SD F-1 Grand Prix - Sample to load and run fine.

That leaves Super Bomberman: Panic Bomber World as the only unplayable title, and Haruka Naru Augusta 3 and Pebble Beach no Hotou as the only two games with "minor" graphical issues. The other 23 SA-1 games should all be fully supported.