Allow generation of vmla.f32 instructions when targeting Cortex-A15. The patch also adds the VFP4 feature to Cortex-A15 and fixes the DontUseFusedMAC predicate so that we can still generate vmla.f32 instructions on non-darwin targets with VFP4.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187349 91177308-0d34-0410-b5e6-96231b3b80d8