At present buildman can compare configurations between commits but the
feature is less useful than it could be. There is no summary by architecture
and changes are not reported on a per-board basis.

Correct these deficiencies so that it is possible to see exactly what is
changing for any number of boards.

Note that 'buildman -b <branch> -C' is recommended for any build where you
will be comparing configuration. Without -C the correct configuration will
not be reported since changes will often not be picked up.

Reviewed-by: Joe Hershberger <joe.hershberger@ni.com>
Signed-off-by: Simon Glass <sjg@chromium.org>