Revert "Update amdgpu_gfx functions to use s0-s3 for inreg SGPR arguments on...

Revert "Update amdgpu_gfx functions to use s0-s3 for inreg SGPR arguments on targets using scratch instructions for stack #78226" (#86273)

Reverts llvm/llvm-project#81394

This reverts commit 3ac243bc.
It is not handling RSrc registers s0-s3 correctly. This leads to a
broken test, where it expects s0-s3 as function argument and uses it as
RSrc register as well.
We need to re-visit the patch, but apparently we only want to have s0-s3
as
argument registers if we don't need them as RSrc registers.