X86: change MOV64ri64i32 into MOV32ri64

The MOV64ri64i32 instruction required hacky MCInst lowering because it was
allocated as setting a GR64, but the eventual instruction ("movl") only set a
GR32. This converts it into a so-called "MOV32ri64" which still accepts a
(appropriate) 64-bit immediate but defines a GR32. This is then converted to
the full GR64 by a SUBREG_TO_REG operation, thus keeping everyone happy.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@182991 91177308-0d34-0410-b5e6-96231b3b80d8