[PowerPC] Extend folding RLWINM + RLWINM to post-RA.

Summary: This patch depends on D89846. We have the patterns to fold 2 RLWINMs in ppc-mi-peephole, while some RLWINM will be generated after RA, for example rGc4690b00. If the RLWINM generated after RA followed by another RLWINM, we expect to perform the optimization after RA, too.

Reviewed By: shchenz, steven.zhang

Differential Revision: https://reviews.llvm.org/D89855