[llvm] [AMDGPU][SIInsertWaitcnts][NFC] Introduce Counter class (PR #190271)

[Shilei Tian via llvm-commits]

shiltian wrote:

Would be helpful if we can have a stack of PRs such that it is clear to see where we are heading and how we are approaching the goal.

https://github.com/llvm/llvm-project/pull/190271