[llvm] [AMDGPU][GFX12] Restrict scalar subword loads to PAL (PR #117576)

[Nicolai Hähnle via llvm-commits]

nhaehnle wrote:

Also, we should not add *more* differences between PAL and other environments. If anything, we should strive to reduce them.

https://github.com/llvm/llvm-project/pull/117576