drm/i915/chv: Enable RPS (Turbo) for Cherryview

v2: Disable media turbo and Add DOWN_IDLE_AVG support (Ville)

v3: Mass rename of the dev_priv->rps variables in upstream.

v4: Rebase against latest code. (Deepak)

v5: Rebase against latest nightly code. (Deepak)

v6: Rename the variables to match the spec (Mika)

v7: change min/max freq variable naming to match spec (Mika)

Signed-off-by: Deepak S <deepak.s@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>