ARM: Let CONFIG_MACH_IMX31_DT be built by default

Let CONFIG_MACH_IMX31_DT be built by default.
Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

arch/arm/configs/imx_v6_v7_defconfig

@@ -19,6 +19,7 @@ CONFIG_MODULE_SRCVERSION_ALL=y
 CONFIG_ARCH_MXC=y
 CONFIG_ARCH_MULTI_V6=y
 CONFIG_ARCH_MULTI_V7=y
+CONFIG_MACH_IMX31_DT=y
 CONFIG_MACH_MX31LILLY=y
 CONFIG_MACH_MX31LITE=y
 CONFIG_MACH_PCM037=y