Seems like your HD7950 (GCN 1.0) doesn't support Freesync according to this very old Tech Site article: https://www.anandtech.com/show/9097/the-amd-freesync-review/5
Besides needing a driver and FreeSync display, you also need a GPU that uses AMD’s GCN 1.1 or later architecture. The list at present consists of the R7 260/260X, R9 285, R9 290/290X/295X2 discrete GPUs, as well as the Kaveri APUs – A6-7400K, A8-7600/7650K, and A10-7700K/7800/7850K. First generation GCN 1.0 cards (HD 7950/7970 or R9 280/280X and similar) are not supported.
Also RAY_M AMD Forum Moderator mentioned the same thing in this old previous AMD Thread: https://community.amd.com/t5/general-discussions/will-gcn-1-0-gpus-will-ever-get-support-for-freesyn...