buildman: Add an option to flatten output directory trees

When building current source for a single board, buildman puts the output
in <output_dir>/current/current/<board>. Add an option to make it use
<output_dir>/<board> instead. This removes the unnecessary directories
in that case, controlled by the --no-subdirs/-N option.

Suggested-by: Tom Rini <trini@ti.com>
Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/buildman/cmdline.py b/tools/buildman/cmdline.py
index 27d3c70..2b75653 100644
--- a/tools/buildman/cmdline.py
+++ b/tools/buildman/cmdline.py
@@ -55,6 +55,8 @@
           help='List available tool chains')
     parser.add_option('-n', '--dry-run', action='store_true', dest='dry_run',
           default=False, help="Do a dry run (describe actions, but do nothing)")
+    parser.add_option('-N', '--no-subdirs', action='store_true', dest='no_subdirs',
+          default=False, help="Don't create subdirectories when building current source for a single board")
     parser.add_option('-o', '--output-dir', type='string',
           dest='output_dir', default='..',
           help='Directory where all builds happen and buildman has its workspace (default is ../)')