[llvm] AMDGPU: Handle folding frame indexes into s_add_i32 (PR #101694)

[Matt Arsenault via llvm-commits]

arsenm wrote:

### Merge activity

* **Aug 22, 1:10 AM EDT**: @arsenm started a stack merge that includes this pull request via [Graphite](https://app.graphite.dev/github/pr/llvm/llvm-project/101694).


https://github.com/llvm/llvm-project/pull/101694