CodeGen: Add MachineInstr::getMF(). NFC

Similarly to how Instruction has getFunction, this adds a less verbose
way to write MI->getParent()->getParent(). I'll follow up shortly with
a change that changes a bunch of the uses.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@315388 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed