[llvm] [AMDGPU]: Rewrite mbcnt_lo/mbcnt_hi to work item ID where applicable (PR #160496)

[Teja Alaghari via llvm-commits]

TejaX-Alaghari wrote:

Thanks @jmmartinez for useful suggestions. I'll implement them and get back soon.

https://github.com/llvm/llvm-project/pull/160496