dt-bindings: add documentation for s3c2412 clock controller

* Samsung S3C2412 Clock Controller

The S3C2412 clock controller generates and supplies clock to various controllers

within the SoC. The clock binding described here is applicable to the s3c2412

and s3c2413 SoCs in the s3c24x family.

Required Properties:

- compatible: should be "samsung,s3c2412-clock"

- 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 can use this identifier

to specify the clock which they consume. Some of the clocks are available only

on a particular SoC.

All available clocks are defined as preprocessor macros in

dt-bindings/clock/s3c2412.h header and can be used in device

tree sources.

External clocks:

There are several clocks that are generated outside the SoC. It is expected

that they are defined using standard clock bindings with following

clock-output-names:

 - "xti" - crystal input - required,

 - "ext" - external clock source - optional,

Example: Clock controller node:

	clocks: clock-controller@4c000000 {

		compatible = "samsung,s3c2412-clock";

		reg = <0x4c000000 0x20>;

		#clock-cells = <1>;

	};

Example: UART controller node that consumes the clock generated by the clock

  controller (refer to the standard clock bindings for information about

  "clocks" and "clock-names" properties):

	serial@50004000 {

		compatible = "samsung,s3c2412-uart";

		reg = <0x50004000 0x4000>;

		interrupts = <1 23 3 4>, <1 23 4 4>;

		clock-names = "uart", "clk_uart_baud2", "clk_uart_baud3";

		clocks = <&clocks PCLK_UART0>, <&clocks PCLK_UART0>,

			 <&clocks SCLK_UART>;

		status = "disabled";

	};