Allwinner RGB LED Driver

The Allwinner LEDC is an high-efficiency RGB LED driver
which is integrated in the SoCs of Allwinner.

Required properties:
	- compatible: "allwinner,sunxi-leds"
	- reg: LEDC registers address.
	- interrupts: the interrupt information for LEDC.
	- interrupt-names: the interrupt name.
	- clocks: the clocks.
	- clock-names: the clock name.
	- pinctrl-names: the pinctrl names.
	- pinctrl-0: the pinctrl which stays in <platform name>-pinctrl.dtsi.

Optional properties:
	- led_count: LED count.
	- output_mode: the mode LEDC output R, G, B data, e.g. if
			the output mode is GRB, LEDC will output
			G data, then R data, and finally B data.
	- trans_mode: the mode that transport R, G, B data from DDR
			to LEDC FIFO, there are two ways: CPU and DMA.
	- reset_ns: the LED reset time in nanoseconds.
	- t1h_ns: 1 code, high level time in nanoseconds.
	- t1l_ns: 1 code, low level time in nanoseconds.
	- t0h_ns: 0 code, high level time in nanoseconds.
	- t0l_ns: 0 code, low level time in nanoseconds.
	- wait_time0_ns: the waiting time in nanoseconds between two LED data.
	- wait_time1_ns: the waiting time in nanoseconds between two frames.
	- wait_data_time_ns: the threshold time that LEDC waiting for the input
			data after LEDC is enabled.

----------------------------Note-------------------------
	Any time parameter has its default value which is
initialized by LEDC hardware, if not assigned in dts, it
will come into the default value got from registers.
---------------------------------------------------------

Example:

sunxi_leds: leds@6 {
	compatible = "allwinner,sunxi-leds";
	reg = <0x0 0x06700000 0x0 0x4c>;
	interrupts = <GIC_SPI 60 IRQ_TYPE_LEVEL_HIGH>;
	interrupt-names = "ledcirq";
	clocks = <&clk_ledc>, <&clk_cpuapb>;
	clock-names = "clk_ledc", "clk_cpuapb";
	pinctrl-names = "default";
	pinctrl-0 = <&ledc_pins_a>;
	led_count = <0x20>;
}