drm/i915: Configure overlay cc_out precision based on crtc gamma config

Put the overlay color conversion unit into 10bit mode if the
pipe isn't using the 8bit legacy gamma. Not 100% sure this is
what the intention of the bit was but makes at least some sense to
me.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191028113036.27553-4-ville.syrjala@linux.intel.com


Acked-by: Chris Wilson <chris@chris-wilson.co.uk>