[PowerPC] Support extended mnemonics mffprwz etc.

Summary:
Reported in https://github.com/opencv/opencv/issues/15413.

We have serveral extended mnemonics for Move To/From Vector-Scalar Register Instructions
eg: mffprd,mtfprd etc.

We only support one of them, this patch add the others.

Reviewers: nemanjai, steven.zhang, hfinkel, #powerpc

Reviewed By: hfinkel

Subscribers: wuzish, qcolombet, hiraditya, kbarton, MaskRay, shchenz, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D66963

llvm-svn: 370411