BCM2835 PWM controller (Raspberry Pi controller)

Required properties:
- compatible: should be "brcm,bcm2835-pwm"
- reg: physical base address and length of the controller's registers
- clocks: This clock defines the base clock frequency of the PWM hardware
  system, the period and the duty_cycle of the PWM signal is a multiple of
  the base period.
- #pwm-cells: Should be 3. See pwm.yaml in this directory for a description of
  the cells format.

Examples:

pwm@2020c000 {
	compatible = "brcm,bcm2835-pwm";
	reg = <0x2020c000 0x28>;
	clocks = <&clk_pwm>;
	#pwm-cells = <3>;
};

clocks {
	....
		clk_pwm: pwm {
			compatible = "fixed-clock";
			reg = <3>;
			#clock-cells = <0>;
			clock-frequency = <9200000>;
		};
	....
};
