[llvm] [mlir] Reland [mlir][amdgpu] Expose waitcnt bitpacking infra (PR #172678)

[Krzysztof Drewniak via llvm-commits]

krzysz00 wrote:

I'd argue that, in that case, you can't build AMDGPUToRocdl if the target isn't being built? Or maybe that's a bit harsh.

https://github.com/llvm/llvm-project/pull/172678