Per latest PM programming guide.

v2: the wrong flavour of the function updating the ring frequency was
    called, leading to dead locks (Tvrtko)

v3: Add GEN6_RP_MEDIA_IS_GFX to RP_CONTROL (Imre, done by Damien)
Signed-off-by: NJesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: NDamien Lespiau <damien.lespiau@intel.com>
Reviewed-by: NMika Kuoppala <mika.kuoppala@intel.com>
[danvet: Fixup conflicts with Mika's forcewake refactor.]
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>