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.

This fixes a typo in the opcode field of the original patch, which
should make the legact JIT work again (& adds test for that problem).