pwm: Add Berlin PWM controller DT binding

Berlin PWM controller

Required properties:

- compatible: should be "marvell,berlin-pwm"

- reg: physical base address and length of the controller's registers

- clocks: phandle to the input clock

- #pwm-cells: should be 3. See pwm.txt in this directory for a description of

  the cells format.

Example:

pwm: pwm@f7f20000 {

	compatible = "marvell,berlin-pwm";

	reg = <0xf7f20000 0x40>;

	clocks = <&chip_clk CLKID_CFG>;

	#pwm-cells = <3>;

}