sh: Fix up rsk7203 target for out of tree build

Fix up rsk7203 target to build successfully using out-of-tree build.

Signed-off-by: Kieran Bingham <kbingham@mpc-data.co.uk>
Signed-off-by: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>
diff --git a/Makefile b/Makefile
index ecde92b..8fb1e2a 100644
--- a/Makefile
+++ b/Makefile
@@ -3230,8 +3230,8 @@
 ## sh2 (Renesas SuperH)
 #########################################################################
 rsk7203_config: unconfig
-	@ >include/config.h
-	@echo "#define CONFIG_RSK7203 1" >> include/config.h
+	@mkdir -p $(obj)include
+	@echo "#define CONFIG_RSK7203 1" > $(obj)/include/config.h
 	@$(MKCONFIG) -a $(@:_config=) sh sh2 rsk7203 renesas
 
 #########################################################################