[llvm] [AMDGPU][SIInsertWaitcnts] Do not add s_waitcnt when the counters are known to be 0 already (PR #72830)

[Jay Foad via llvm-commits]

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

I think this is OK to commit now.

I'm still a little confused about why we promote soft waitcnts in two places, but at worst one of them is redundant and everything should still work correctly.

https://github.com/llvm/llvm-project/pull/72830