Extend GBA memory map to include non-mapped ranges

[Drakmyth]

While RAM digging a GBA game, I came across a number of values that looked suspiciously like pointers except that they began with 0x04 and 0x08 prefixes, but as this documentation suggested I would only see 0x02, 0x03, and 0x0e prefixes I was confused about what I was seeing. A helpful soul on the RA discord kindly provided me with a more detailed memory map that explained I was seeing pointers to I/O and ROM.

Although such pointers can't be accessed by achievements, having these ranges documented so developers can understand what they are seeing is extremely helpful.