binman: Check missing bintools of Section subclasses

Binman can check for missing binary tools and prints warnings if
anything required for an image is missing. The implementation of this
for the Section entry only checks the subentries, presumably because
Section does not use any binary tools itself. However, this means the
check is also skipped for subclasses of Section which might need binary
tools.

Make sure missing binary tools are checked for subclasses of the Section
entry type as well, by calling the parent class' implementation in
the relevant Section method.

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