drm/i915: Extract icl_color_check()

ICL is rather easy when it comes to .color_check() as it
finally provides us with a full color pipeline with
individual knobs for each stage.

We'll also start bypassing each LUT individually when
it is not needed.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190327155045.28446-6-ville.syrjala@linux.intel.com