dt-bindings: can: tcan4x5x: Document the wakeup-source flag

Let it be known that the tcan4x5x device can now be configured to wake
the host from suspend when a can frame is received.
Signed-off-by: Martin Hundebøll <martin@geanix.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
[mkl: make first the first patch]
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

Documentation/devicetree/bindings/net/can/tcan4x5x.txt

@@ -28,6 +28,8 @@ Optional properties:
 			      available with tcan4552/4553.
 	- device-wake-gpios: Wake up GPIO to wake up the TCAN device. Not
 			     available with tcan4552/4553.
+	- wakeup-source: Leave the chip running when suspended, and configure
+			 the RX interrupt to wake up the device.
 
 Example:
 tcan4x5x: tcan4x5x@0 {
@@ -42,4 +44,5 @@ tcan4x5x: tcan4x5x@0 {
 		device-state-gpios = <&gpio3 21 GPIO_ACTIVE_HIGH>;
 		device-wake-gpios = <&gpio1 15 GPIO_ACTIVE_HIGH>;
 		reset-gpios = <&gpio1 27 GPIO_ACTIVE_HIGH>;
+		wakeup-source;
 };