[llvm] AMDGPU/GlobalISel: Handle atomic sextload and zextload (PR #111721)

[Matt Arsenault via llvm-commits]

arsenm wrote:

### Merge activity

* **Oct 31, 10:38 AM EDT**: A user started a stack merge that includes this pull request via [Graphite](https://app.graphite.dev/github/pr/llvm/llvm-project/111721).


https://github.com/llvm/llvm-project/pull/111721