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

[via llvm-commits]

SahilPatidar wrote:

@arsenm,
here are a few expected failed cases. Let me know if they need to be updated.
```
Total Discovered Tests: 3484
  Unsupported      :   49 (1.41%)
  Passed           : 3429 (98.42%)
  Expectedly Failed:    6 (0.17%)
```

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