drm/edid: Introduce drm_default_rgb_quant_range()

Make the code selecting the RGB quantization range a little less magicy
by wrapping it up in a small helper.

v2: s/adjusted_mode/mode in vc4 to make it actually compile
v3: Add a comment proposed by Eric

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170111141835.25369-1-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Acked-by: Eric Anholt <eric@anholt.net>
diff --git a/include/drm/drm_edid.h b/include/drm/drm_edid.h
index 838eaf2..25cdf5f 100644
--- a/include/drm/drm_edid.h
+++ b/include/drm/drm_edid.h
@@ -441,6 +441,8 @@
 bool drm_detect_hdmi_monitor(struct edid *edid);
 bool drm_detect_monitor_audio(struct edid *edid);
 bool drm_rgb_quant_range_selectable(struct edid *edid);
+enum hdmi_quantization_range
+drm_default_rgb_quant_range(const struct drm_display_mode *mode);
 int drm_add_modes_noedid(struct drm_connector *connector,
 			 int hdisplay, int vdisplay);
 void drm_set_preferred_mode(struct drm_connector *connector,