[llvm] [AMDGPU][NFC] Move InstCounterType and Waitcnt to SIInsertWaitcnts.h (PR #187823)

[via llvm-commits]

vporpo wrote:

> The file does expose a thing called a Waitcnt, and so the name of the file should be Waitcnt.h. It really has nothing to do with the pass, and I am not okay with the current name.

The header file does not expose only the Waitcnt class but also things related to InstrCounterType, which are only used in SIInsertWaitcnt, and they only really make sense in the context of the SIInsertWaitcnts pass. So I think Waitcnt.h is not very suitable name in this case, which is why I renamed the file to SIInsertWaitcnts.h.

@jayfoad @arsenm any thoughts on the name of the header file?

https://github.com/llvm/llvm-project/pull/187823