ZTE ZX PWM controller

Required properties:
 - compatible: Should be "zte,zx296718-pwm".
 - reg: Physical base address and length of the controller's registers.
 - clocks : The phandle and specifier referencing the controller's clocks.
 - clock-names: "pclk" for PCLK, "wclk" for WCLK to the PWM controller.  The
   PCLK is for register access, while WCLK is the reference clock for
   calculating period and duty cycles.
 - #pwm-cells: Should be 3. See pwm.yaml in this directory for a description of
   the cells format.

Example:

	pwm: pwm@1439000 {
		compatible = "zte,zx296718-pwm";
		reg = <0x1439000 0x1000>;
		clocks = <&lsp1crm LSP1_PWM_PCLK>,
			 <&lsp1crm LSP1_PWM_WCLK>;
		clock-names = "pclk", "wclk";
		#pwm-cells = <3>;
	};