[llvm] [AMDGPU] Shrink to SOPK with 32-bit signed literals (PR #70263)

[Jay Foad via llvm-commits]

https://github.com/jayfoad approved this pull request.

I'm a bit surprised it doesn't affect any codegen tests.

Anyway makes sense to me since the src operand of S_MOVK_I32 is signed but the src operand of S_MOV_B32 is not (B32 is neither signed nor unsigned, but I guess we generally treat it like unsigned).

https://github.com/llvm/llvm-project/pull/70263