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

Specify clock property in binding.
Signed-off-by: Srinivas Neeli <srinivas.neeli@xilinx.com>
Acked-by: Michal Simek <michal.simek@xilinx.com>
Link: https://lore.kernel.org/r/1605201148-4508-3-git-send-email-srinivas.neeli@xilinx.comSigned-off-by: Linus Walleij <linus.walleij@linaro.org>

Documentation/devicetree/bindings/gpio/gpio-xilinx.txt

@@ -13,6 +13,7 @@ Required properties:
 - 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
@@ -29,6 +30,7 @@ Example:
 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 >;