buildman: Add an option to just create the config

Normally buildman does a full build of a board. This includes creating the
u-boot.cfg file which contains all the configuration options. Buildman uses
this file with the -K option, to show differences in effective configuration
for each commit.

Doing a full build of U-Boot just to create the u-boot.cfg file is wasteful.
Add a -D option which causes buildman to only create the configuration. This
is enough to support use of -K and can be done much more quickly (typically
5-10 times faster).

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

tools/buildman/cmdline.py

@@ -28,6 +28,8 @@ def ParseArgs():
     parser.add_option('-d', '--detail', dest='show_detail',
           action='store_true', default=False,
           help='Show detailed information for each board in summary')
+    parser.add_option('-D', '--config-only', action='store_true', default=False,
+          help="Don't build, just configure each commit")
     parser.add_option('-e', '--show_errors', action='store_true',
           default=False, help='Show errors and warnings')
     parser.add_option('-f', '--force-build', dest='force_build',