binman: Allow listing an image created by a newer version

binman: Allow listing an image created by a newer version

If an older version of binman is used to list images created by a newer
one, it is possible that it will contain entry types that are not
supported. At present this produces an error.

Adjust binman to use a plain 'blob' entry type to cope with this, so the
image can at least be listed.

Signed-off-by: Simon Glass <sjg@chromium.org>