buildman: Squash useless output from -K

When using #define CONFIG_SOME_OPTION, the value it set to '1'. When using
defconfig (i.e. CONFIG_SOME_OPTION=y) the value is set to 'y'. This results
in differences showing up with -K. These differences are seldom useful.

Adjust buildman to suppress these differences by default.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/buildman/cmdline.py b/tools/buildman/cmdline.py
index bd3776a..0060e03 100644
--- a/tools/buildman/cmdline.py
+++ b/tools/buildman/cmdline.py
@@ -59,6 +59,8 @@
           default=False, help='Keep all build output files (e.g. binaries)')
     parser.add_option('-K', '--show-config', action='store_true',
           default=False, help='Show configuration changes in summary (both board config files and Kconfig)')
+    parser.add_option('--preserve-config-y', action='store_true',
+          default=False, help="Don't convert y to 1 in configs")
     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,