I was having this problem where my blender 2.8 didn't recognize my GPU driver.
I have a AMD RX 580 and my operating system is Ubuntu 18.04. For those who have this same problem I will post it as an answer below.
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First you have to download and install the AMD pro drivers for your GPU here.
If you're using Linux you just extract it and open the terminal inside the folder you just extracted. Type in the terminal
./amdgpu-pro-install --opencl=pal,legacy,rocm and hit enter. It is very important to put the opencl options. That was the reason why I was trying to install and reinstall my GPU drivers and nothing happened.
Restart your pc and check your GPU options in blender.
I hope this helps all Linux users facing this problem.
Found this solution here.