drm/i915: Update pipe gamma enable bits when C8 planes are getting enabled/disabled

drm/i915: Update pipe gamma enable bits when C8 planes are getting enabled/disabled

When the first C8 plane gets enabled, or the last one gets disabled we
may need to enable/disable the pipe gamma for the other active planes.
Check for that and run through the normal intel_color_check() path.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190513133904.20374-2-ville.syrjala@linux.intel.com
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>