UNIF: Fix potential crash when accessing non-existing rom banks

- As stated, prevent a potential crash on some certain roms using split rom banks. This is done by counting the number of prg/chr banks loaded and using this as limit count during mapper bank switching.
- Update related boards.

src/boards/ax40g.c

@@ -88,8 +88,3 @@ void UNLAX40G_Init(CartInfo *info) {
 	GameStateRestore = StateRestore;
 	AddExState(&StateRegs, ~0, 0, 0);
 }
-
-/*void UNLAX40G_Init(CartInfo *info);			// m527
-{ "AX-40G", UNLAX40G_Init, 0 },
-{ "JC-016-2", Mapper205_Init, 0 },
-*/