[NFC][PowerPC] Move the folding RLWINMs from ppc-mi-peephole to PPCInstrInfo.

[NFC][PowerPC] Move the folding RLWINMs from ppc-mi-peephole to PPCInstrInfo.

Summary: We have the patterns to fold 2 RLWINMs in ppc-mi-peephole, while some RLWINM will be generated after RA, for example D88274. If the RLWINM generated after RA followed by another RLWINM, we expect to perform the optimization after RA, too.
This is a NFC patch to move the folding patterns to PPCInstrInfo, and the follow-up works will be calling it in pre-emit-peephole and expand the patterns to handle more cases.

Reviewed By: shchenz

Differential Revision: https://reviews.llvm.org/D89846