[PowerPC] Eliminate integer compare instructions - vol. 2

This patch builds upon https://reviews.llvm.org/rL302810 to add
handling for bitwise logical operations in general purpose registers.
The idea is to keep the values in GPRs as long as possible - only
extracting them to a condition register bit when no further operations
are to be done.

Differential Revision: https://reviews.llvm.org/D31851

llvm-svn: 304282