ARM: mxs: always build in device tree support

As the ultimate for mxs platform is to convert over to device tree,
let's start always building in device tree support for the platform.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Acked-by: Marek Vasut <marex@denx.de>
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index ae5c251..1f1a4fa 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -471,6 +471,7 @@
 	select COMMON_CLK
 	select HAVE_CLK_PREPARE
 	select PINCTRL
+	select USE_OF
 	help
 	  Support for Freescale MXS-based family of processors