clk: versatile: Add SP810 device tree bindings document

Signed-off-by: NPawel Moll <pawel.moll@arm.com>
Signed-off-by: NStephen Boyd <sboyd@codeaurora.org>

Documentation/devicetree/bindings/arm/sp810.txt

+SP810 System Controller
+-----------------------
+
+Required properties:
+
+- compatible:	standard compatible string for a Primecell peripheral,
+		see Documentation/devicetree/bindings/arm/primecell.txt
+		for more details
+		should be: "arm,sp810", "arm,primecell"
+
+- reg:		standard registers property, physical address and size
+		of the control registers
+
+- clock-names:	from the common clock bindings, for more details see
+		Documentation/devicetree/bindings/clock/clock-bindings.txt;
+		should be: "refclk", "timclk", "apb_pclk"
+
+- clocks:	from the common clock bindings, phandle and clock
+		specifier pairs for the entries of clock-names property
+
+- #clock-cells: from the common clock bindings;
+		should be: <1>
+
+- clock-output-names: from the common clock bindings;
+		should be: "timerclken0", "timerclken1", "timerclken2", "timerclken3"
+
+Example:
+	sysctl@020000 {
+		compatible = "arm,sp810", "arm,primecell";
+		reg = <0x020000 0x1000>;
+		clocks = <&v2m_refclk32khz>, <&v2m_refclk1mhz>, <&smbclk>;
+		clock-names = "refclk", "timclk", "apb_pclk";
+		#clock-cells = <1>;
+		clock-output-names = "timerclken0", "timerclken1", "timerclken2", "timerclken3";
+	};