buildman: Only print toolchain probing with -v

At present --list-tool-chains prints a lot of information about the
toolchain-probing process. This is generally not very interesting.
Update buildman to print this only if --list-tool-chains is given
with -v.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/buildman/cmdline.py b/tools/buildman/cmdline.py
index 49a8a13..93d09ca 100644
--- a/tools/buildman/cmdline.py
+++ b/tools/buildman/cmdline.py
@@ -66,7 +66,7 @@
     parser.add_option('-l', '--list-error-boards', action='store_true',
           default=False, help='Show a list of boards next to each error/warning')
     parser.add_option('--list-tool-chains', action='store_true', default=False,
-          help='List available tool chains')
+          help='List available tool chains (use -v to see probing detail)')
     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',