Remove getARMRegisterNumbering and replace with calls into

Remove getARMRegisterNumbering and replace with calls into
the register info for getEncodingValue. This builds on the
small patch of yesterday to set HWEncoding in the register
file.

One (deprecated) use was turned into a hard number to avoid
needing register info in the old JIT.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@161628 91177308-0d34-0410-b5e6-96231b3b80d8