arm, suen3: fix compile error, if doing not a local build

Signed-off-by: Heiko Schocher <hs@denx.de>
diff --git a/board/keymile/km_arm/Makefile b/board/keymile/km_arm/Makefile
index fffc6a3..c5b0be1 100644
--- a/board/keymile/km_arm/Makefile
+++ b/board/keymile/km_arm/Makefile
@@ -23,6 +23,9 @@
 #
 
 include $(TOPDIR)/config.mk
+ifneq ($(OBJTREE),$(SRCTREE))
+$(shell mkdir -p $(obj)../common)
+endif
 
 LIB	= $(obj)lib$(BOARD).a