drm/edid: Introduce drm_hdmi_avi_infoframe_quant_range()

Pull the logic to populate the quantization range information
in the AVI infoframe into a small helper. We'll be adding a bit
more logic to it, and having it in a central place seems like a
good idea since it's based on the CEA-861 spec.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170111125725.8086-4-ville.syrjala@linux.intel.com


Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Acked-by: Eric Anholt <eric@anholt.net>