Remove the MachineMove class.

It was just a less powerful and more confusing version of
MCCFIInstruction. A side effect is that, since MCCFIInstruction uses
dwarf register numbers, calls to getDwarfRegNum are pushed out, which
should allow further simplifications.

I left the MachineModuleInfo::addFrameMove interface unchanged since
this patch was already fairly big.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@181680 91177308-0d34-0410-b5e6-96231b3b80d8