Mask GetPointer Differently on GameCube

[JMC47]

GameCube can't access EXRAM I'm guessing, so we need to wrap it different. Number was verified by LibOGC or something by someone who wasn't me.

Fixes Starfox Assault crash better this time.

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This change is

[BhaaLseN]

That comment was what got me the idea of doing this in here; and the mask 0x01ffffff is the next-best thing for the amount of physically available RAM on a GameCube.
I suppose it still applies though, since we don't exactly know if that covers all cases; and we still have games/cases where it doesn't affect enough to fix things. Somewhere else in that file, it mentions that the whole function is just a guesstimation of what could be.

Should probably be "mask", not "wrap" tho ;)

[shuffle2]

These masks should probably be derived from Memory::REALRAM_SIZE or something (or else MP3 beta will break 😛 )

[JMC47]

Right. If I could modify this to work with Metroid Prime 3's Beta, that'd be even better. Is there a way to do that?

[JMC47]

Note: Metroid Prime 3's beta doesn't run right now without modifying Dolphin, so if I can kill two birds with one stone, I definitely will. It'd make a good video.

[shuffle2]

converting the enum values into variables should be possible without too much trouble, but I'd be willing to bet there will be some perf impact, since the values are used in a bunch of pretty hot code paths.

Someone should try it, I guess ;)

[JMC47]

This PR is wrong, 24/32 MB is open bus.