clk: ux500: Add device tree bindings for ABx500 clocks

This adds device tree bindings for the ABx500 clocks on the
ST-Ericsson platforms.

Cc: devicetree@vger.kernel.org
Acked-by: NUlf Hansson <ulf.hansson@linaro.org>
Acked-by: NRob Herring <robh@kernel.org>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>
Signed-off-by: NStephen Boyd <sboyd@codeaurora.org>

Documentation/devicetree/bindings/clock/stericsson,abx500.txt

+Clock bindings for ST-Ericsson ABx500 clocks
+
+Required properties :
+- compatible : shall contain the following:
+  "stericsson,ab8500-clk"
+- #clock-cells should be <1>
+
+The ABx500 clocks need to be placed as a subnode of an AB8500
+device node, see mfd/ab8500.txt
+
+All available clocks are defined as preprocessor macros in
+dt-bindings/clock/ste-ab8500.h header and can be used in device
+tree sources.
+
+Example:
+
+clock-controller {
+	compatible = "stericsson,ab8500-clk";
+	#clock-cells = <1>;
+};