[llvm] [RFC][AMDGPU][InsertWaitCnt] Move WaitEventType into separate HWEvent header (PR #202886)

[Pierre van Houtryve via llvm-commits]

================

----------------
Pierre-vh wrote:

The separate def file is a bit cleaner IMO. We don't need to use the .def file in multiple headers to make it worth it. For example: 
- llvm/lib/Target/AMDGPU/AMDGPUAttributes.def
- llvm/lib/Target/AMDGPU/AMDGPUPassRegistry.def

In this case we also need to be aware of the first/last element, if I just use macros to get rid of this one file, it creates a big macro soup which isn't very clear.

If you strongly feel the .def shouldn't be there I can remove it

https://github.com/llvm/llvm-project/pull/202886