[llvm] AMDGPU: Add more tests for peephole-opt immediate folding (PR #127480)

[Matt Arsenault via llvm-commits]

arsenm wrote:

### Merge activity

* **Feb 17, 10:28 PM EST**: A user started a stack merge that includes this pull request via [Graphite](https://app.graphite.dev/github/pr/llvm/llvm-project/127480).


https://github.com/llvm/llvm-project/pull/127480