[clang] [llvm] [AMDGPU] Add support for `v_cos_bf16` on gfx1250 (PR #149355)

[Shilei Tian via cfe-commits]

shiltian wrote:

### Merge activity

* **Jul 17, 6:41 PM UTC**: A user started a stack merge that includes this pull request via [Graphite](https://app.graphite.dev/github/pr/llvm/llvm-project/149355).


https://github.com/llvm/llvm-project/pull/149355