am335x: configure tca6416 interrupt

I've an am335x-based board with tca6416. OS: Linux with kernel 3.14. The interrupt output of the
tca6416 is connected to GPIO0_20 on my SoC. How should I configure this
wiring in a device tree file?

I've already managed to hook it on I2C and it is working so far:

 tca6416: gpio@20 {
                compatible = "ti,tca6416";
                reg = <0x20>;
                gpio-controller;
                #gpio-cells = <2>;
  };

Documentation/devicetree/bindings/gpio/gpio-pcf857x.txt describes
following properties:

  - interrupt-controller: Identifies the node as an interrupt controller.
  - #interrupt-cells: Number of cells to encode an interrupt source, shall be 2.
  - interrupt-parent: phandle of the parent interrupt controller.
  - interrupts: Interrupt specifier for the controllers interrupt.

and following example:

        pcf8575: gpio@20 {
                compatible = "nxp,pcf8575";
                reg = <0x20>;
                interrupt-parent = <&irqpin2>;
                interrupts = <3 0>;
                gpio-controller;
                #gpio-cells = <2>;
                interrupt-controller;
                #interrupt-cells = <2>;
        };

Where does irqpin2 come from? How to specify GPIO0_20 in "interrupts" context?