serial: mxs: Add MXS AUART driver

Add trivial driver for the MXS AUART IP. This is the other UART IP
present in i.MX23 and i.MX28, used to drive the non-DUART ports.

Signed-off-by: Marek Vasut <marex@denx.de>
diff --git a/drivers/serial/Makefile b/drivers/serial/Makefile
index 01fef3f..403ab1d 100644
--- a/drivers/serial/Makefile
+++ b/drivers/serial/Makefile
@@ -46,6 +46,7 @@
 obj-$(CONFIG_BCM283X_PL011_SERIAL) += serial_bcm283x_pl011.o
 obj-$(CONFIG_MSM_SERIAL) += serial_msm.o
 obj-$(CONFIG_MSM_GENI_SERIAL) += serial_msm_geni.o
+obj-$(CONFIG_MXS_AUART_SERIAL) += serial_mxs.o
 obj-$(CONFIG_MVEBU_A3700_UART) += serial_mvebu_a3700.o
 obj-$(CONFIG_MPC8XX_CONS) += serial_mpc8xx.o
 obj-$(CONFIG_NULLDEV_SERIAL) += serial_nulldev.o