drm/edid: abstract cea data block collection size

Add a function to get the cea data block collection size.

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/5339ab3249400a3c41001967e7ff2611b58e0425.1654674560.git.jani.nikula@intel.com