[llvm] [TableGen] Emit OpName as an enum class instead of a namespace (PR #125313)

[Jay Foad via llvm-commits]

https://github.com/jayfoad commented:

> jayfoad any feedback on the AMDGPU side?

I only skimmed the AMDGPU changes but they look great to me overall, assuming the rest of the patch is accepted.

https://github.com/llvm/llvm-project/pull/125313