To mine on Linux with your card you need to use the proprietary Catalyst 15.9 driver or 15.12 beta driver.
https://support.amd.com/en-us/download/desktop/previous/detail?os=Linux+x86_64&rev=15.9https://support.amd.com/en-us/kb-articles/Pages/AMDRadeonSoftwareCrimsonEdition15-12LINReleaseNotes.aspxThose are the last drivers to support OpenCL for your card on Linux. The newer open source AMDGPU Linux driver doesn't support AMD APP-SDK OpenCL and the AMDGPU PRO proprietary driver for newer AMD Radeon cards on Linux doesn't support your card.
The problem is you will also have to downgrade to Ubuntu 15.10 since the older Catalyst 15.12 driver doesen't support Xorg >1.17.
I had the same problem on Arch Linux since I have a HD 7850 and found out when I added an RX 480 that the newer AMDGPU Pro proprietary driver doesen't support GCN 1 or GCN 2 cards on Linux. I ultimately had to switch to mining on Windows to keep mining with all my cards. Thanks AMD!
https://wiki.archlinux.org/index.php/Xorg#AMD