[llvm] [NFC][AMDGPU] Guard FP8 related instructions properly (PR #115211)

[Shilei Tian via llvm-commits]

shiltian wrote:

### Merge activity

* **Nov 7, 12:18 PM EST**: A user started a stack merge that includes this pull request via [Graphite](https://app.graphite.dev/github/pr/llvm/llvm-project/115211).


https://github.com/llvm/llvm-project/pull/115211