clk: ux500: Add device tree bindings for ABx500 clocks

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>;

};