[ARM] Minor cleanup to lXX and stX. Fixes a bug.
Fixes an issue in lXX where if the instruction was an update instruction and was a register address offset that we would add garbage values to the
writeback register.
Does some minor cleanups as well which save a few instructions here and there.
[ARM] Implements more fastmem instructions in lXX.
There are a few instructions in lXX that aren't currently fastmem capable due to using a register offset.
This implements fastmem for those few instructions.
Really I'll be changing how ARMv7 fastmem works in the future so this is really temporary code.
Just don't know how long it'll stay.
This relies on PR #257