[llvm] [AMDGPU] Callee saves for amdgpu_cs_chain[_preserve] (PR #71526)

[Nicolai Hähnle via llvm-commits]

https://github.com/nhaehnle approved this pull request.

I'm not an expert on the callee-saved logic, but to me it looks good.

https://github.com/llvm/llvm-project/pull/71526