armemu: Simplify REVSH/UXTH/UXTAH
armemu: Simplify USAT16/UXTB/UXTAB
armemu: Simplify REV/REV16/SXTH/SXTAH
armemu: Simplify SSAT/SSAT16/SXTB/SXTAB
Merge pull request #355 from lioncash/simp

armemu: Simplify some instructions.