tty/serial: of_serial: add DT alias ID handling

Add support for alias parsing from the DT. This allows for consistent
tty numbering.

Signed-off-by: Rob Herring <robh@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: linux-serial@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/of_serial.c

@@ -128,6 +128,10 @@ static int of_platform_serial_setup(struct platform_device *ofdev,
 	if (of_find_property(np, "no-loopback-test", NULL))
 		port->flags |= UPF_SKIP_TEST;
 
+	ret = of_alias_get_id(np, "serial");
+	if (ret >= 0)
+		port->line = ret;
+
 	port->dev = &ofdev->dev;
 
 	switch (type) {