AMDGPU/EG: Add a new FeatureFMA and use it to selectively enable FMA instruction

Only used by pre-GCN targets
v2: fix predicate setting for FMA_Common

Differential Revision: https://reviews.llvm.org/D40692

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@319712 91177308-0d34-0410-b5e6-96231b3b80d8
7 files changed