[llvm] AMDGPU: Add support for V_CVT_PK_F16_F32 instruction for gfx950 (PR #118300)

[Matt Arsenault via llvm-commits]

arsenm wrote:

### Merge activity

* **Dec 2, 4:03 PM EST**: A user started a stack merge that includes this pull request via [Graphite](https://app.graphite.dev/github/pr/llvm/llvm-project/118300).


https://github.com/llvm/llvm-project/pull/118300