Rockchip PWM controller

Required properties:
- compatible: should be "rockchip,<name>-pwm"
- reg: physical base address and length of the controller's registers
- #pwm-cells: should be 2.  The first cell specifies the per-chip index
  of the PWM to use and the second cell is the period in nanoseconds.
- pinctrl-names: must contain a "default" entry.
- pinctrl-0: the pincontrol settings to configurethe.
- clocks: phandle to the PWM source clock
- clock-names: list of clock names sorted in the same order as the clocks.
- status: for device state control (enabled/disabled).

Example:

pwm1: pwm@53fb4000 {
	#pwm-cells = <2>;
	compatible = "fsl,imx53-pwm", "fsl,imx27-pwm";
	reg = <0x53fb4000 0x4000>;
	interrupts = <61>;
};
pwm0: pwm@ff680000 {
	compatible = "rockchip,rk-pwm";                                                                                                                                    
	reg = <0xff680000 0x10>;                                                                                                                                           
	#pwm-cells = <2>;                                                                                                                                                  
	pinctrl-names = "default";                                                                                                                                         
	pinctrl-0 = <&pwm0_pin>;                                                                                                                                           
	clocks = <&clk_gates11 11>;                                                                                                                                        
	clock-names = "pclk_pwm";                                                                                                                                          
	status = "disabled";                                                                                                                                               
};