drm: add the VIC number to the CEA EDID modes

The specification defines a VIC (Video Identification Code) for each
mode. When we're browsing drm_edid_modes.h, it really helps to have the
number available (otherwise we have to count...). These numbers are also
used in the EDID data (by the CEA-EXT extension block).
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Adam Jackson <ajax@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>