[llvm] [AMDGPU] Promote uniform ops to i32 in GISel (PR #106557)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm commented:

Should add a MIR test that ensures this doesn't crash on a preset register class.

The codegen changes look worse to me, and I don't see any improvements. I think the issue is this is trying to promote after regbankselect, when most of the legalization up to scalar operations already occurred 

https://github.com/llvm/llvm-project/pull/106557