dt-bindings: usb: usb251xb: add documentation for data lane swapping

Add optional binding to allow USB differential-pair (D+/D-) data lane
swapping. The swapping can be specified for each port separately,
default is no swapping.

Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
Reviewed-by: Richard Leitner <richard.leitner@skidata.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/usb/usb251xb.txt

@@ -64,6 +64,8 @@ Optional properties :
  - power-on-time-ms : Specifies the time it takes from the time the host
 	initiates the power-on sequence to a port until the port has adequate
 	power. The value is given in ms in a 0 - 510 range (default is 100ms).
+ - swap-dx-lanes : Specifies the ports which will swap the differential-pair
+	(D+/D-), default is not-swapped.
 
 Examples:
 	usb2512b@2c {
@@ -81,4 +83,6 @@ Examples:
 		manufacturer = "Foo";
 		product = "Foo-Bar";
 		serial = "1234567890A";
+		/* correct misplaced usb connectors on port 1,2 */
+		swap-dx-lanes = <1 2>;
 	};