Rename regs (remove .r and .n suffix for reg types). [Not for merging]

Regs can now be accessed directly by name or by array index when specifying the reg type.
This removes a lot of the 'fluff'.

Any discussion on renaming of regs is welcome.

Only GPR and CP0 use named entries. The names are quite different and relate to actual reg functions, so hard to be confused. Even so, perhaps the names should be changed in some instances.
It would likely be better as an enum.
Hmm.  Personally, I think these changes make things more readable but maybe go too far.

`psxRegs.GPR.n.v0` is definitely ugly looking.  Though it's longer, I prefer what we use in PPSSPP - `psxRegs.r[MIPS_REG_V0]`.

Maybe a best of both worlds would be to define GPRRegs as a struct, and give it v0, etc. but also an index/pointer operator?  Then you could have `psxRegs.GPR[#]` and `psxRegs.GPR.v0`.

GPR vs v0 (rather than gpr/v0 or GPR/V0) seems odd to me, but that's existing.

I think the same goes for the other regs: having them namespaced under CP0/etc. is likely still valuable.  The extra step of n/r/etc. is just cruft.

-[Unknown]