[PowerPC] [NFC] Add AIX triple to some regression tests

[PowerPC] [NFC] Add AIX triple to some regression tests

As part of the effort to improve AIX support, regression test coverage
misses quite a lot for AIX subtarget. This patch adds AIX triple to
those don't need extra change, and we can cover more cases in following
commits.

Reviewed By: steven.zhang

Differential Revision: https://reviews.llvm.org/D94159