dt-bindings: mfd: rn5t618: Document optional property interrupts

These chips use interrupts for various things like RTC alarm.
Signed-off-by: Andreas Kemnade <andreas@kemnade.info>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

Documentation/devicetree/bindings/mfd/rn5t618.txt

@@ -15,6 +15,8 @@ Required properties:
  - reg: the I2C slave address of the device
 
 Optional properties:
+ - interrupts: interrupt mapping for IRQ
+   See Documentation/devicetree/bindings/interrupt-controller/interrupts.txt
  - system-power-controller:
    See Documentation/devicetree/bindings/power/power-controller.txt
 
@@ -32,6 +34,8 @@ Example:
 	pmic@32 {
 		compatible = "ricoh,rn5t618";
 		reg = <0x32>;
+		interrupt-parent = <&gpio5>;
+		interrupts = <11 IRQ_TYPE_EDGE_FALLING>;
 		system-power-controller;
 
 		regulators {