drm/i915: Separate RPS and RC6 handling for VLV

drm/i915: Separate RPS and RC6 handling for VLV

This patch separates enable/disable of RC6 and RPS for VLV.

v2: Removed unnecessary comments about forcewakes while enabling
RC6/RPS. Added changes to output turbo control status for VLV in
i915_frequency_info.

Signed-off-by: Sagar Arun Kamble <sagar.a.kamble@intel.com>
Cc: Imre Deak <imre.deak@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Radoslaw Szwichtenberg <radoslaw.szwichtenberg@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/1507360055-19948-5-git-send-email-sagar.a.kamble@intel.com
Acked-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20171010213010.7415-4-chris@chris-wilson.co.uk