ARM: mxs_defconfig: Let AUART driver be built by default

Let AUART driver be built by default.
Signed-off-by: NFabio Estevam <fabio.estevam@freescale.com>
Reviewed-by: NMarek Vasut <marex@denx.de>
Signed-off-by: NShawn Guo <shawn.guo@linaro.org>

arch/arm/configs/mxs_defconfig

@@ -81,6 +81,7 @@ CONFIG_DEVPTS_MULTIPLE_INSTANCES=y
 # CONFIG_DEVKMEM is not set
 CONFIG_SERIAL_AMBA_PL011=y
 CONFIG_SERIAL_AMBA_PL011_CONSOLE=y
+CONFIG_SERIAL_MXS_AUART=y
 # CONFIG_HW_RANDOM is not set
 CONFIG_I2C=y
 # CONFIG_I2C_COMPAT is not set