ARM: make arch_ret_to_user macro optional

Only 3 platforms need arch_ret_to_user macro, so add ARCH_HAS_RET_TO_USER
kconfig option and make iop13xx, iop32x and iop33x select it.

Signed-off-by: Rob Herring <rob.herring@calxeda.com>
Acked-by: Nicolas Pitre <nico@linaro.org>
diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
index 9fd0ba9..54ee265 100644
--- a/arch/arm/kernel/entry-common.S
+++ b/arch/arm/kernel/entry-common.S
@@ -10,9 +10,15 @@
 
 #include <asm/unistd.h>
 #include <asm/ftrace.h>
-#include <mach/entry-macro.S>
 #include <asm/unwind.h>
 
+#ifdef CONFIG_NEED_RET_TO_USER
+#include <mach/entry-macro.S>
+#else
+	.macro  arch_ret_to_user, tmp1, tmp2
+	.endm
+#endif
+
 #include "entry-header.S"