drm/i915: Clean up DP/HDMI limited color range handling

Currently we treat intel_{dp,hdmi}->color_range as partly user
controller value (via the property) but we also change it during
.compute_config() when using the "Automatic" mode. That is a bit
confusing, so let's just change things so that we store the user
property values in intel_dp, and only change what's stored in
pipe_config during .compute_config().

There should be no functional change.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Sivakumar Thulasimani <sivakumar.thulasimani@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>