Tegra SoC PWFM controller

Required properties:
- compatible: should be one of:
  - "nvidia,tegra20-pwm"
  - "nvidia,tegra30-pwm"
- reg: physical base address and length of the controller's registers
- #pwm-cells: On Tegra the number of cells used to specify a PWM is 2. The
  first cell specifies the per-chip index of the PWM to use and the second
  cell is the duty cycle in nanoseconds.

Example:

	pwm: pwm@7000a000 {
		compatible = "nvidia,tegra20-pwm";
		reg = <0x7000a000 0x100>;
		#pwm-cells = <2>;
	};
