[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, 
why are some test updates crashing with this output:
Assertion failed: (Reg != AMDGPU::NoRegister), function allocateFixedSGPRInputImpl, file /Users/sahilpatidar/Desktop/llvm/llvm-project/llvm/lib/Target/AMDGPU/SIISelLowering.cpp, line 2292.

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