Makefile: remove generated boards.cfg within make distclean

Signed-off-by: Roger Meier <roger@bufferoverflow.ch>
Reviewed-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Tested-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Cc: Tom Rini <trini@ti.com>
Cc: Wolfgang Denk <wd@denx.de>
Cc: Simon Glass <sjg@chromium.org>
diff --git a/Makefile b/Makefile
index b5b3560..0f82fc2 100644
--- a/Makefile
+++ b/Makefile
@@ -1289,6 +1289,7 @@
 		-o -name '.*.rej' -o -name '*%' -o -name 'core' \
 		-o -name '*.pyc' \) \
 		-type f -print | xargs rm -f
+	@rm -f boards.cfg
 
 backup:
 	F=`basename $(srctree)` ; cd .. ; \