#7 Change SRAM banks to support Bridge

[Anonymous]

Modify Pogoshell source to utilize SRAM bank 2 for
unpacking and banks 3 & 4 for storing saves.
This would leave bank 1 untouched by the Pogoshell
system, so that the GB Bridge could utilize it without
corrupting GBA saves and vice-versa.
Until a fast/playable GB emulator becomes available,
this is the only way to ensure saves from Gameboy
Advance games and Gameboy/Gameboy Color and co-
exist happily.