[clang] [llvm] [AMDGPU] Add support for `v_cvt_f16_fp8` on gfx1250 (PR #146302)

[Shilei Tian via cfe-commits]

shiltian wrote:

### Merge activity

* **Jun 30, 11:47 AM UTC**: A user started a stack merge that includes this pull request via [Graphite](https://app.graphite.dev/github/pr/llvm/llvm-project/146302).


https://github.com/llvm/llvm-project/pull/146302