drm/i915: Enable fine-tuned RPS for cherryview

drm/i915: Enable fine-tuned RPS for cherryview

When the RPS tuning was applied to Baytrail, in commit 2db0188ebfd7
("drm/i915: Agressive downclocking on Baytrail"), concern was given that
it might cause Cherryview excess wakeups of the common power well.
However, the static thresholds perform poorly for Kodi, and the GPU is
unable to deliver the video frames on time. Enabling the dynamic, finer
thresholds used on all other platforms (including Skylake and Broxton
that also have the same multiple powerwell concerns) allows the GPU to
pick a more appropriate frequency and not drop frames.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/20170210150348.22146-1-chris@chris-wilson.co.uk
Reviewed-by: Radoslaw Szwichtenberg <radoslaw.szwichtenberg@intel.com>