dt-bindings: gpio: gpio-xilinx: Add clk support to xilinx soft gpio IP

- gpio-controller : Marks the device node as a GPIO controller.

Optional properties:

- clocks : Input clock specifier. Refer to common clock bindings.

- interrupts : Interrupt mapping for GPIO IRQ.

- xlnx,all-inputs : if n-th bit is setup, GPIO-n is input

- xlnx,dout-default : if n-th bit is 1, GPIO-n default value is 1

gpio: gpio@40000000 {

	#gpio-cells = <2>;

	compatible = "xlnx,xps-gpio-1.00.a";

	clocks = <&clkc25>;

	gpio-controller ;

	interrupt-parent = <&microblaze_0_intc>;

	interrupts = < 6 2 >;