[PowerPC] Run reg2mem on tests to simplify them.

Summary:
Also convert test/CodeGen/PowerPC/vsx-ldst-builtin-le.ll to use
FileCheck instead of two grep and count runs.

This change is needed to avoid spurious diffs in these tests when
EarlyCSE is improved to use MemorySSA and can do more load elimination.

Reviewers: hfinkel

Subscribers: mcrosier, llvm-commits

Differential Revision: http://reviews.llvm.org/D20238

llvm-svn: 271553