i#1551 port to ARM: SIMD sub-reg mappings

Put in proper reg_fixer mappings for the AArch32 SIMD sub-reg mappings,
which double-up rather than just representing the bottom portion of the
same-numbered larger register.

git-svn-id: https://dynamorio.googlecode.com/svn/trunk@2958 49cc7528-f6fd-11dd-9d1a-b59b2e1864b6