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

[Jay Foad via llvm-commits]

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

Looks OK to me, though I'd be happier if it was approved by someone more of a memory model expert than me.

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