dt-binding: rng: Add interrupt property for BCM2835

As Sylvain Garrigues pointed out the BCM2835 RNG block has an
interrupt. Also in preparation for Florian's upcoming patch series
add this property to the binding. While we are at it fix the
indenting of the example.

Link: https://github.com/raspberrypi/linux/issues/2195
CC: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: NStefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: NFlorian Fainelli <f.fainelli@gmail.com>

Documentation/devicetree/bindings/rng/brcm,bcm2835.txt

@@ -14,11 +14,16 @@ Optional properties:
 - clocks : phandle to clock-controller plus clock-specifier pair
 - clock-names : "ipsec" as a clock name
 
+Optional properties:
+
+- interrupts: specify the interrupt for the RNG block
+
 Example:
 
 rng {
 	compatible = "brcm,bcm2835-rng";
 	reg = <0x7e104000 0x10>;
+	interrupts = <2 29>;
 };
 
 rng@18033000 {