[X86] Cleanup fma tests a little bit. NFC.

Reformat, isolate 213->231 xform, actually --check-prefix CHECK,
and deduplicate the FMA intrinsic tests (FMA3 in AMD-land).


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@240615 91177308-0d34-0410-b5e6-96231b3b80d8
6 files changed