Mesa doesn't provide OpenCL 1.2 support for Navi
AMD provide closed-source AMDGPU-PRO OpenCL 2.0 (PAL for Vega and Navi and Legacy for older product)
Alternatively you can use open-sourced AMD Radeon Open Compute platforM with OpenCL 2.0 support (Hardware Support)
It doesn't breaks Mesa/LLVM dependencies or UEFI Secure Boot