X86: Fix bugs in movd implementation.

X86: Fix bugs in movd implementation.

Unfortunately my implementation of the movd instruction had two bugs.

In one case, when moving a 32-bit value into an xmm register, the
lower half of the xmm register was not zero extended.

The other case is that xmm was used instead of xmmlm as the source
for a register move.  My test case didn't notice this at first
as it moved xmm0 to eax, which both have the same register
number.