[PowerPC][Peephole] Combine rldicl/rldicr and andi/andis after isel.

Summary: rldicl/rldicr can be eliminated if it's used to clear the high-order or low-order n bits and all bits cleared will be ANDed with 0 by andi/andis. Or they can be folded to `andi 0` if all bits to AND are already zero in the input.

Reviewed By: qiucf, shchenz

Differential Revision: https://reviews.llvm.org/D159073