[llvm] [AMDGPU] Define constrained multi-dword scalar load instructions. (PR #96161)

[Christudasan Devadasan via llvm-commits]

cdevadas wrote:

### Merge activity

* **Jul 23, 4:02 AM EDT**: @cdevadas started a stack merge that includes this pull request via [Graphite](https://app.graphite.dev/github/pr/llvm/llvm-project/96161).


https://github.com/llvm/llvm-project/pull/96161