TI SOC EHRPWM based PWM controller

Required properties:
- compatible: Must be "ti,<soc>-ehrpwm".
  for am33xx - compatible = "ti,am33xx-ehrpwm";
  for da850  - compatible = "ti,da850-ehrpwm", "ti,am33xx-ehrpwm";
  for dra7xx - compatible = "ti,dra7xx-ehrpwm", "ti,am33xx-ehrpwm";
- #pwm-cells: should be 3. See pwm.txt in this directory for a description of
  the cells format. The only third cell flag supported by this binding is
  PWM_POLARITY_INVERTED.
- reg: physical base address and size of the registers map.

Optional properties:
- clocks: Reference to the ehrpwm's tb clock
- clock-names : must contain "tbclk"

Example:

ehrpwm0: pwm@48300200 { /* EHRPWM on am33xx */
	compatible = "ti,am33xx-ehrpwm";
	#pwm-cells = <3>;
	reg = <0x48300200 0x100>;
	clocks = <&ehrpwm0_tbclk>;
	clock-names = "tbclk";
};

ehrpwm0: pwm@01f00000 { /* EHRPWM on da850 */
	compatible = "ti,da850-ehrpwm", "ti,am33xx-ehrpwm";
	#pwm-cells = <3>;
	reg = <0x300000 0x2000>;
};

ehrpwm0: pwm@4843e200 { /* EHRPWM on dra7xx */
	compatible = "ti,dra7xx-ehrpwm", "ti,am33xx-ehrpwm";
	#pwm-cells = <3>;
	reg = <0x48440200 0x80>;
	clocks = <&ehrpwm0_tbclk>;
	clock-names = "tbclk";
};