Moving D122765 along (AMDGPU dialect, including some vendor-specific wrappers)

⚙ D122765 [MLIR][AMDGPU] Add AMDGPU dialect, wrappers around raw buffer intrinsics adds MLIR-ic wrappers around some AMDGPU-specific LLVM intrinsics and sets up the dialect so we can put a few more such wrappers into it.

While I’ve gotten some comments, I haven’t had any firm movement on this revision for a while and I’d like to make sure there’s progress.