Add casts to MEM_ macros

[AngheloAlf]

Added gpr casts to the arguments of the MEM_ macros to ensure the arithmetic is done as 64bits instead of something dumb because the caller passed 32bits unsigned values or similar. I also added ULL suffix to those big constants in the macro to ensure nothing will do something dumb.

I also changed save_write to use a size_t instead of uint32_t because that's the function that gave me problems in the first place

This PR was originally made in Zelda64Recomp/Zelda64Recomp#136