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/control.py b/tools/buildman/control.py
index 0b3ba94..545c2cb 100644
--- a/tools/buildman/control.py
+++ b/tools/buildman/control.py
@@ -259,7 +259,8 @@
             verbose_build=options.verbose_build,
             incremental=options.incremental,
             per_board_out_dir=options.per_board_out_dir,
-            config_only=options.config_only)
+            config_only=options.config_only,
+            squash_config_y=not options.preserve_config_y)
     builder.force_config_on_failure = not options.quick
     if make_func:
         builder.do_make = make_func