drm/edid: add #defines for ELD versions

Add ELD versions according to HDA Specification v1.0a.

2 indicates version 2, which supports CEA_Ver 861D or below. Maximum
Baseline ELD size of 80 bytes (15 SAD count).

31 indicates an ELD that has been partially populated through
implementation specific mean of default programming before an external
graphics driver is loaded. Only the field that is called out as "canned"
field will be populated, and audio driver should ignore the non "canned"
field.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>