Replace vfmaddxx213 instructions with their 231-type equivalents in accumulator
loops. Writing back to the accumulator (231-type) allows the coalescer to
eliminate an extra copy.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@199933 91177308-0d34-0410-b5e6-96231b3b80d8