drm/edid: convert add_cea_modes() to use cea db iter

Iterate through all CTA EDID extension blocks and DisplayID CTA data
blocks to add CEA modes.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/dfa2d79db61d5eea543bef7aca7d80da3e71f99d.1651569697.git.jani.nikula@intel.com