UbuntuFriend

Oland XT [Radeon HD 8670 / R7 250/350] video cards are supported by amdgpu module which comes with the Linux kernel. By default if the radeon module is loading first then you need to disable it and then make the amdgpu module load first.
Also sudo  apt install mesa-opencl-icd clinfo
If you do not have cl headers then install the using "sudo apt install opencl-clhpp-headers opencl-c-headers "
 
This is also a good GPU to start learning opencl since this one has 6 CU and over 1Gb VRAM that can be used as a global memory, to speed up your calculations you might want to learn how to keep array in the __local or __private memory, that way you will get at least order of magnitude more speed.