[PEI] Remove required properties and use 'if' instead of std::function

Summary:
After r303360, we initialize UsesCalleeSaves in runOnMachineFunction,
which runs after getRequiredProperties. UsesCalleeSaves was initialized
to 'false', so getRequiredProperties would always return an empty set.
We don't have a TargetMachine available early anymore after r303360.
Just removing the requirement of NoVRegs seems to make things work, so
let's do that.

Reviewers: thegameg, dschuff, MatzeB

Subscribers: hiraditya, llvm-commits

Differential Revision: https://reviews.llvm.org/D38597

llvm-svn: 315089