Lower formal arguments and returns for functions with the
amdgpu_cs_chain and amdgpu_cs_chain_preserve calling conventions:
- Put inreg arguments into SGPRs, starting at s0, and other arguments
into VGPRs, starting at v8. No arguments should end up on the stack, if
we don't have enough registers we should error out.
- Lower the return (which is always void) as an S_ENDPGM.
- Set the ScratchRSrc register to s48:51, as described in the docs.
- Set the SP to s32.
Just remove the assert, I don't see anything actually preventing usage right now pre-gfx9 and this would need to be a proper error