There is initial support for AMD "Sea Islands" hardware and there's also Active State Power Management support. The move shows how the adoption of Linux software options by Steam has forced AMD to focus on Linux more enthusiastically. Radeon Linux users have been screaming for all this stuff, along with faster OpenGL performance, for ages. The best that AMD has given them is limited static power management and no dynamic re-clocking based upon load.
The Catalyst driver has supported dynamic power management via "PowerPlay" for years, but there's never been nice open-source GPU driver power management. Patches can for now be found on the dri-devel list here.