AMDGPU: Replace fp16SrcZerosHighBits with a whitelist

FCOPYSIGN is lowered to bit operations which don't clear the high
bits.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@299708 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed