dt-bindings: Document the hi3660 clock bindings

* Hisilicon Hi3660 Clock Controller

The Hi3660 clock controller generates and supplies clock to various

controllers within the Hi3660 SoC.

Required Properties:

- compatible: the compatible should be one of the following strings to

	indicate the clock controller functionality.

	- "hisilicon,hi3660-crgctrl"

	- "hisilicon,hi3660-pctrl"

	- "hisilicon,hi3660-pmuctrl"

	- "hisilicon,hi3660-sctrl"

	- "hisilicon,hi3660-iomcu"

- reg: physical base address of the controller and length of memory mapped

  region.

- #clock-cells: should be 1.

Each clock is assigned an identifier and client nodes use this identifier

to specify the clock which they consume.

All these identifier could be found in <dt-bindings/clock/hi3660-clock.h>.

Examples:

	crg_ctrl: clock-controller@fff35000 {

		compatible = "hisilicon,hi3660-crgctrl", "syscon";

		reg = <0x0 0xfff35000 0x0 0x1000>;

		#clock-cells = <1>;

	};

	uart0: serial@fdf02000 {

		compatible = "arm,pl011", "arm,primecell";

		reg = <0x0 0xfdf02000 0x0 0x1000>;

		interrupts = <GIC_SPI 74 IRQ_TYPE_LEVEL_HIGH>;

		clocks = <&crg_ctrl HI3660_CLK_MUX_UART0>,

			 <&crg_ctrl HI3660_PCLK>;

		clock-names = "uartclk", "apb_pclk";

		status = "disabled";

	};