buildman: Show board list with -x

When -x is used, buildman does not show the list of boards that will be
built, since there are no terms which cause boards to be added, only
terms which cause them to be removed.

Add a special case to fix this.

Signed-off-by: Simon Glass <sjg@chromium.org>
Tested-by: Tom Rini <trini@konsulko.com>
1 file changed