Disable a couple more vector splat optimizations on PPC.

I didn't see those because the test case used "not grep". FileCheck the test and
XFAIL it, preserving the old optimization, so this can be fixed eventually.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@174330 91177308-0d34-0410-b5e6-96231b3b80d8