[PPC] Adjust some PowerPC tests to account for presence/absence of VSX

[PPC] Adjust some PowerPC tests to account for presence/absence of VSX

Patch by Bill Seurer; committed on his behalf.

These test cases generate slightly different code sequences when VSX
is activated and thus fail. The update turns off VSX explicitly for
the existing checks and then adds a second set of checks for most of
them that test the VSX instruction output.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@220019 91177308-0d34-0410-b5e6-96231b3b80d8