[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,
for this test function `define void @void_func_a13i32_inreg([13  x i32] inreg %arg0, ptr addrspace(1) %ptr)`

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