Split MachineLICM into EarlyMachineLICM and MachineLICM; NFC

This avoids playing games with pseudo pass IDs and avoids using an
unreliable MRI::isSSA() check to determine whether register allocation
has happened.

Note that this renames:
- MachineLICMID -> EarlyMachineLICM
- PostRAMachineLICMID -> MachineLICMID
to be consistent with the EarlyTailDuplicate/TailDuplicate naming.

llvm-svn: 322927