serial: support 16-bit register interface for console

Currently, 8-bit (MMIO) and 32-bit (MMIO32) register interfaces are
supported for the 8250 console, but the 16-bit (MMIO16) is not.
The 8250 UART device on my board is connected to a 16-bit bus and
my main motivation is to use earlycon with it.
(Refer to arch/arm/boot/dts/uniphier-support-card.dtsi)

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/tty/serial/of_serial.c b/drivers/tty/serial/of_serial.c
index de50296..6d002ee 100644
--- a/drivers/tty/serial/of_serial.c
+++ b/drivers/tty/serial/of_serial.c
@@ -122,6 +122,9 @@
 		case 1:
 			port->iotype = UPIO_MEM;
 			break;
+		case 2:
+			port->iotype = UPIO_MEM16;
+			break;
 		case 4:
 			port->iotype = of_device_is_big_endian(np) ?
 				       UPIO_MEM32BE : UPIO_MEM32;