[llvm] Update amdgpu_gfx functions to use s0-s3 for inreg SGPR arguments on targets using scratch instructions for stack #78226 (PR #81394)

[Thomas Symalla via llvm-commits]

tsymalla wrote:

Hi @arsenm  @SahilPatidar Please take a look at the referenced revert PR #86273, since the change introduced here breaks some tests.

https://github.com/llvm/llvm-project/pull/81394