NXP PCA9685 16-channel 12-bit PWM LED controller
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Required properties:
  - compatible: "nxp,pca9685-pwm"
  - #pwm-cells: Should be 2. See pwm.yaml in this directory for a description of
    the cells format.
    The index 16 is the ALLCALL channel, that sets all PWM channels at the same
    time.
Optional properties:
  - invert (bool): boolean to enable inverted logic
  - open-drain (bool): boolean to configure outputs with open-drain structure;
		       if omitted use totem-pole structure
Example:
For LEDs that are directly connected to the PCA, the following setting is
applicable:
pca: pca@41 {
	compatible = "nxp,pca9685-pwm";
	#pwm-cells = <2>;
	reg = <0x41>;
	invert;
	open-drain;
};