[PowerPC][NFC] Avoid checking non-relevant .cfi instructions

Summary:
This is brought up in
https://reviews.llvm.org/D64662?id=209923#inline-599490

CFI information are non-relevant to quite some testcases,
we should get rid of checking them when its unecessary.

This patch avoid generating cfi info in testcases that are not
testing prolog/epilog or exception handling.

Reviewers: kbarton, hfinkel, nemanjai, #powerpc

Reviewed By: hfinkel

Subscribers: MaskRay, shchenz, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D67016

llvm-svn: 370505