Add description for out of bounds MBC ram access

[alloncm]

This is based on:

• Source code of the SameBoy emulator
• Disassembling Pokemon Pinball which depends on this behavior
• Mbc1 schematics - https://www.devrs.com/gb/files/mbc1.gif

Since there are many types of MBC's I added that this is for most of the MBC's

[nummacway]

Use "modulo max_ram_size" instead of "and (max_ram_size - 1)"?
Why does Pinball depend on it? It doesn't even have banked RAM.

[alloncm]

Perhaps "depends" is not the best way to phrase it, what I actually saw is that Pokemon Pinball sets the ram bank to a non zero value and since it does not have banked ram, all accesses are clipped (according to the formula).
Failing to emulate this exact behavior causes the game to freeze at some point.

[nummacway]

What point? I want to try with a 32 KiB cart.

[alloncm]

It depends on the way you are handling this case, originally I just ignored those out of bounds writes, (and returned 0 on reads) with this way it froze after trying to reload a save from sram (boot up -> save -> restart -> load save -> freeze).
I dont remember exactly if the load save is also done with the same non zero bank (I think it was bank 4) if it is it supposed to work with a 32kb cart, if not I think it will freeze.