ARM64: Improve diagnostics for malformed reg+reg addressing mode.

Make sure only general purpose registers are valid for offset regs and
that 32-bit regs are only valid for sxtw and uxtw extends.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206799 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed