dt-bindings: power: supply: axp20x_usb_power: add axp813 compatible

This adds the "x-powers,axp813-usb-power-supply" to the list of
compatibles for AXP20X VBUS power supply driver.
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

Documentation/devicetree/bindings/power/supply/axp20x_usb_power.txt

@@ -4,6 +4,7 @@ Required Properties:
 -compatible: One of: "x-powers,axp202-usb-power-supply"
                      "x-powers,axp221-usb-power-supply"
                      "x-powers,axp223-usb-power-supply"
+		     "x-powers,axp813-usb-power-supply"
 
 The AXP223 PMIC shares most of its behaviour with the AXP221 but has slight
 variations such as the former being able to set the VBUS power supply max