PowerPCState register (and rationalize register usage, and add some registers to replace it)

See the commits!
After this PR is merged, I'll take a whack at converting other pointer accesses from jit'd code (for aslr, because hey, why not?). It also results in cleaner looking emitted code, and from my experiments based on an older version of this PR, it's actually not that hard.  
Anyways, I think "missed" opportunities aren't a big deal with this PR. That being said, I'm sure it's just as easy for the regex-replace to be done in either PR.