[llvm] [AMDGPU] Relax SOPK immediate signed/unsigned check (PR #77015)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm commented:

The MIR verifier has no bearing on the assembler support. This check is for our own sanity, so we should just be better about marking instructions with sopkIsZext 

https://github.com/llvm/llvm-project/pull/77015