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

[Stanislav Mekhanoshin via llvm-commits]

rampitec wrote:

I just wish to have some optimization here: most of these loads are from kernarg. We know that kernarg is page aligned (I guess?). We also know a minimal page size and kernarg size. So if kernarg size is no greater than page size, skip it. Or if kernarg is not page aligned, make it page aligned.

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