I'm running ubuntu 18.04.3 LTS kernel 5.0.0-25-generic, I use to have 18.50-756341 which works well with my Radeon VII and my rx 550.
I've removed drv 18.50-756341, then I installed 19.30-838629.
When running clinfo, it only detects the 'PAL' platform of the radeon VII, not the 'legacy' one for RX 550, same for RX 580.
I've also tried with 19.30-855429 same issue.
It seems OpenCL support for Polaris is missing in this driver.