tools: genboardscfg: move buildman path to first

To system which has kconfiglib installed, genboardscfg will
use system kconfiglib, we need it use U-Boot owned version,
so move the buildman path to first.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Cc: Masahiro Yamada <yamada.m@jp.panasonic.com>
Cc: Simon Glass <sjg@chromium.org>
Cc: Tom Rini <trini@konsulko.com>
Acked-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/genboardscfg.py b/tools/genboardscfg.py
index 0648472..e9bbd15 100755
--- a/tools/genboardscfg.py
+++ b/tools/genboardscfg.py
@@ -24,7 +24,7 @@
 import tempfile
 import time
 
-sys.path.append(os.path.join(os.path.dirname(__file__), 'buildman'))
+sys.path.insert(1, os.path.join(os.path.dirname(__file__), 'buildman'))
 import kconfiglib
 
 ### constant variables ###