That feature is not in master yet. You may checkout agd-powerplay branch in git://people.freedesktop.org/~agd5f/xf86-video-ati or agd-powerplay branch in git://people.freedesktop.org/~csimpson/xf86-video-ati
You won't be able to change the power profile live, you will have to restart the server
That branch is basically a proof of concept. It only implements sclk, mclk, and pcie lane adjustments statically based on the mode you select in your xorg.conf. There's a lot more involved. There is currently no interface in X to do this dynamically, so I've been looking at implementing it the radeon kms drm. Then userspace utilities like gnome-power-manager can adjust power policy on the fly.