Add support for VSX FMA single-precision instructions to the PPC back end

Add support for VSX FMA single-precision instructions to the PPC back end

This patch corresponds to review:
http://reviews.llvm.org/D9941

It adds the various FMA instructions introduced in the version 2.07 of
the ISA along with the testing for them. These are operations on single
precision scalar values in VSX registers.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@238578 91177308-0d34-0410-b5e6-96231b3b80d8