dt-bindings: add documentation for Exynos3250 clock controller

The Exynos3250 clocks are statically listed and registered using the
Samsung specific common clock helper functions. Both device tree based
clock lookup and clkdev based clock lookups are supported.
Signed-off-by: NChanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: NTomasz Figa <t.figa@samsung.com>
Acked-by: NKyungmin Park <kyungmin.park@samsung.com>
Cc: Mike Turquette <mturquette@linaro.org>
Cc: Kukjin Kim <kgene.kim@samsung.com>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Pawel Moll <pawel.moll@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Ian Campbell <ijc+devicetree@hellion.org.uk>
Cc: Kumar Gala <galak@codeaurora.org>
Cc: Randy Dunlap <rdunlap@infradead.org>
Acked-by: NTomasz Figa <t.figa@samsung.com>
Signed-off-by: NKukjin Kim <kgene.kim@samsung.com>

Documentation/devicetree/bindings/clock/exynos3250-clock.txt

+* Samsung Exynos3250 Clock Controller
+
+The Exynos3250 clock controller generates and supplies clock to various
+controllers within the Exynos3250 SoC.
+
+Required Properties:
+
+- compatible: should be one of the following.
+  - "samsung,exynos3250-cmu" - controller compatible with Exynos3250 SoC.
+
+- 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.
+
+All available clocks are defined as preprocessor macros in
+dt-bindings/clock/exynos3250.h header and can be used in device
+tree sources.
+
+Example 1: An example of a clock controller node is listed below.
+
+	cmu: clock-controller@10030000 {
+		compatible = "samsung,exynos3250-cmu";
+		reg = <0x10030000 0x20000>;
+		#clock-cells = <1>;
+	};
+
+Example 2: 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' property.
+
+	serial@13800000 {
+		compatible = "samsung,exynos4210-uart";
+		reg = <0x13800000 0x100>;
+		interrupts = <0 109 0>;
+		clocks = <&cmu CLK_UART0>, <&cmu CLK_SCLK_UART0>;
+		clock-names = "uart", "clk_uart_baud0";
+	};