ARM: imx_v6_v7_defconfig: Select CONFIG_SOC_IMX6SX

Let mx6sx be built by default.
Signed-off-by: NFabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: NShawn Guo <shawn.guo@freescale.com>

arch/arm/configs/imx_v6_v7_defconfig

@@ -37,6 +37,7 @@ CONFIG_SOC_IMX50=y
 CONFIG_SOC_IMX53=y
 CONFIG_SOC_IMX6Q=y
 CONFIG_SOC_IMX6SL=y
+CONFIG_SOC_IMX6SX=y
 CONFIG_SOC_VF610=y
 CONFIG_PCI=y
 CONFIG_PCI_IMX6=y