I believe you have to install "amdgpu-pro" if you want GPU acceleration in SVP as the default mesa implementation of OpenCL for AMD graphics is pretty much broken and/or majorly outdated.
(I unfortunately have no modern discrete AMD GPUs so I can't actually confirm/refute this...)
Sadly I installed amdgpu-pro & it didn't work.
I'm currently using AMD Fluid Motion which is much better in resource usage & less artifacts.
It's literally awesome