- Add TargetInstrInfo::isIdentical(). It's similar to MachineInstr::isIdentical

- Add TargetInstrInfo::isIdentical(). It's similar to MachineInstr::isIdentical
  except it doesn't care if the definitions' virtual registers differ. This is
  used by machine LICM and other MI passes to perform CSE.
- Teach Thumb2InstrInfo::isIdentical() to check two t2LDRpci_pic are identical.
  Since pc relative constantpool entries are always different, this requires it
  it check if the values can actually the same.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@86328 91177308-0d34-0410-b5e6-96231b3b80d8