[PowerPC] Implement isMaskAndCmp0FoldingBeneficial

Sinking the and closer to a compare against zero is beneficial on PPC as it
allows us to emit record-form instructions. In the future, we may expand this
to a larger set of operations that feed compares against zero since PPC has
lots of record-form instructions.

Differential revision: https://reviews.llvm.org/D46060

llvm-svn: 331416