[llvm] [AMDGPU][SIMemoryLegalizer][GFX12] Correctly insert sample/bvhcnt (PR #161637)

[Pierre van Houtryve via llvm-commits]

Pierre-vh wrote:

> What would be a good place to define "correctly insert samplecnt/bvhcnt"? I believe the patch inserts these waitcnts for all releases and seq_cst operations, but not for acquire operations. Is that the intention? Is this documented somewhere?

It's in AMDGPUUsage, this patch just makes SIMemoryLegalizer honor it.
Before it was inserting those SAMPLE/BVHcnt and they were eliminated by InsertWaitCnt, now SIMemoryLegalizer does it right the first time

I'll improve the description

https://github.com/llvm/llvm-project/pull/161637