dt-bindings: tcan4x5x: Make wake-gpio an optional gpio

The wake-up of the device can be configured as an optional feature of
the device. Move the wake-up gpio from a requried property to an
optional property.
Signed-off-by: Dan Murphy <dmurphy@ti.com>
Cc: Rob Herring <robh@kernel.org>
Reviewed-by: Sean Nyekjaer <sean@geanix.com>
Tested-by: Sean Nyekjaer <sean@geanix.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

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

@@ -10,7 +10,6 @@ Required properties:
 	- #size-cells: 0
 	- spi-max-frequency: Maximum frequency of the SPI bus the chip can
 			     operate at should be less than or equal to 18 MHz.
-	- device-wake-gpios: Wake up GPIO to wake up the TCAN device.
 	- interrupt-parent: the phandle to the interrupt controller which provides
                     the interrupt.
 	- interrupts: interrupt specification for data-ready.
@@ -23,6 +22,7 @@ Optional properties:
 		       reset.
 	- device-state-gpios: Input GPIO that indicates if the device is in
 			      a sleep state or if the device is active.
+	- device-wake-gpios: Wake up GPIO to wake up the TCAN device.
 
 Example:
 tcan4x5x: tcan4x5x@0 {