ARM: mvebu: Add Core Divider clock device-tree binding

* Core Divider Clock bindings for Marvell MVEBU SoCs

The following is a list of provided IDs and clock names on Armada 370/XP:

 0 = nand (NAND clock)

Required properties:

- compatible : must be "marvell,armada-370-corediv-clock"

- reg : must be the register address of Core Divider control register

- #clock-cells : from common clock binding; shall be set to 1

- clocks : must be set to the parent's phandle

Example:

corediv_clk: corediv-clocks@18740 {

	compatible = "marvell,armada-370-corediv-clock";

	reg = <0x18740 0xc>;

	#clock-cells = <1>;

	clocks = <&pll>;

};