[llvm] AMDGPU: Add more mfma with constant splat input tests (PR #140581)

[Matt Arsenault via llvm-commits]

arsenm wrote:

### Merge activity

* **May 19, 3:39 PM EDT**: A user started a stack merge that includes this pull request via [Graphite](https://app.graphite.dev/github/pr/llvm/llvm-project/140581).


https://github.com/llvm/llvm-project/pull/140581