ARM: imx_v6_v7_defconfig: enable psci default

i.MX7D uboot support psci firmware.
Enabled psci default.
Signed-off-by: Frank Li <Frank.Li@freescale.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm/configs/imx_v6_v7_defconfig

@@ -47,6 +47,7 @@ CONFIG_PCI=y
 CONFIG_PCI_MSI=y
 CONFIG_PCI_IMX6=y
 CONFIG_SMP=y
+CONFIG_ARM_PSCI=y
 CONFIG_PREEMPT_VOLUNTARY=y
 CONFIG_AEABI=y
 CONFIG_HIGHMEM=y