Move -widen-vmovs to ARMBaseInstrInfo::expandPostRAPseudo().

The VMOVS widening needs to look at the implicit COPY operands.  Trying
to dig out the COPY instruction from an iterator in copyPhysReg() is the
wrong approach.

The expandPostRAPseudo() hook gets to look at COPY instructions before
they are converted to copyPhysReg() calls.

llvm-svn: 141619