Enable frameskipping in the null gpu.

In case it's used (I used it to check cpu-only perf on Android.)
armjit: Refer to R11 as MEMBASEREG for clarity.
Return the correct value for fcr0/fir.

This is what the PSP actually returns, it's read only.
Fix handling of jalr when delay slot changes rd.
armjit: Read fpu control regs other than 0/31 as 0.

Always seem to give zero, regardless of the value of fcr31, etc.
Initialize fcr31 correctly (even though unsup.)
Mask out fcr31 bits that can't be set on a PSP.
Merge pull request #4543 from unknownbrackets/cpu-minor

Minor cpu correctness adjustments