readelf: add pretty printing for FDO Dlopen Metadata note

readelf: add pretty printing for FDO Dlopen Metadata note

The node ID and the string format are now fixed, even if the content
of the string might change, it will still be a string.

     * libebl/eblobjnote.c (ebl_object_note): Handle both type
     being NT_FDO_PACKAGING_METADATA or NT_FDO_DLOPEN_METADATA when
     name is "FDO".
     * libebl/eblobjnotetypename.c (ebl_object_note_type_name): Handle
     "FDO" name and type NT_FDO_DLOPEN_METADATA.

Signed-off-by: Luca Boccassi <bluca@debian.org>