Add small ARM perf experiment. Did not help on ARMv7 so turned it off.

xsacha might want to try it on ARMv6.
This variant didn't seem to make much difference either (see prev commit)
Optimize mfv/mtv/mfc1/mtc1 on x86 too
Fix bug from a couple of commits ago in ARMJit
x86 jit: Rename BindToRegister to MapReg
ARM regcache: Add mechanism to keep registers converted to pointers around