moffset forms of moves are x86-32 only, make the parser

moffset forms of moves are x86-32 only, make the parser
lower them to the correct x86-64 instructions since we
don't have a clean way to handle this in td files yet.
rdar://7947184

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@103668 91177308-0d34-0410-b5e6-96231b3b80d8