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

[Stanislav Mekhanoshin via llvm-commits]

rampitec wrote:

> The buffer instructions aren't constrained yet. Can I do that in a separate patch?
Yes, this is a note, not required for this patch.


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