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

[Ivan Butygin via llvm-commits]

Hardcode84 wrote:

I can wrap entire `AMDGPUToROCDL` part into `if(MLIR_ENABLE_ROCM_CONVERSIONS)` which depends on LLVM target being enabled.

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