ARM: multi_v7_defconfig: Build in CONFIG_GPIO_MXC by default

i.MX SoC GPIO driver provides the basic functions of GPIO pin operations
and IRQ operations, it is now changed from "def_bool y" to "tristate", so
it should be explicitly enabled to make sure all consumers work normally.
Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm/configs/multi_v7_defconfig

@@ -465,6 +465,7 @@ CONFIG_GPIO_PALMAS=y
 CONFIG_GPIO_TPS6586X=y
 CONFIG_GPIO_TPS65910=y
 CONFIG_GPIO_TWL4030=y
+CONFIG_GPIO_MXC=y
 CONFIG_POWER_AVS=y
 CONFIG_ROCKCHIP_IODOMAIN=y
 CONFIG_POWER_RESET_AS3722=y