[llvm] [AMDGPU] Split struct kernel arguments (PR #133786)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm requested changes to this pull request.

I'd rather avoid having an ABI breaking pass, and I definitely want to avoid spreading the handling of non-byref kernel arguments. This has overlap with the existing IR expansion of non-byref arguments 

https://github.com/llvm/llvm-project/pull/133786