binman: Rename ExpandToLimit to extend_to_limit

The word 'expand' is used for entries which generate subentries. It is
also used for entries that can have an '_expanded' version which is used
to break out its contents.

Rather than talking about expanding an entry's size, use the term
'extending'. It is slightly more precise and avoids the above conflicts.

This change renders the old 'expand-size' property invalid, so add an
error check for that.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Alper Nebi Yasak <alpernebiyasak@gmail.com>