[AMDGPU] Handle f16 select{_cc}

- Select `select` to `v_cndmask_b32`
- Expand `select_cc`
- Refactor patterns

Differential Revision: https://reviews.llvm.org/D26714


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@287074 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed