[llvm] [openacc][openmp] Add dialect representation for acc atomic operations (PR #65493)

[Guray Ozen via llvm-commits]

grypp wrote:

Hey, I've just seen this PR, I understand the need for a common atomic interface between these two models. 

I am little concerned about the `OpenACCMPCommon` folder is in the `dialect` folder, but there is no dialect definition here? There is a single interface `AtomicInterface`, imho atomics can be used beyond just OpenACC/MP. 

Would make sense to delete the `OpenACCMPCommon` folder and move the `AtomicInterface` to the `include/mlir/interfaces`? 

https://github.com/llvm/llvm-project/pull/65493