Binding for the HSDK Generic PLL clock

This binding uses the common clock binding[1].

[1] Documentation/devicetree/bindings/clock/clock-bindings.txt

Required properties:
- compatible: should be "snps,hsdk-<name>-pll-clock"
  "snps,hsdk-core-pll-clock"
  "snps,hsdk-gp-pll-clock"
  "snps,hsdk-hdmi-pll-clock"
- reg : should contain base register location and length.
- clocks: shall be the input parent clock phandle for the PLL.
- #clock-cells: from common clock binding; Should always be set to 0.

Example:
	input_clk: input-clk {
		clock-frequency = <33333333>;
		compatible = "fixed-clock";
		#clock-cells = <0>;
	};

	cpu_clk: cpu-clk@0 {
		compatible = "snps,hsdk-core-pll-clock";
		reg = <0x00 0x10>;
		#clock-cells = <0>;
		clocks = <&input_clk>;
	};
