DT: leds: Add bindings for ISSI is31fl319x

LEDs connected to is31fl319x LED controller chip

Required properties:

- compatible : Should be any of

	"issi,is31fl3190"

	"issi,is31fl3191"

	"issi,is31fl3193"

	"issi,is31fl3196"

	"issi,is31fl3199"

	"si-en,sn3199".

- #address-cells: Must be 1.

- #size-cells: Must be 0.

- reg: 0x64, 0x65, 0x66, or 0x67.

Optional properties:

- audio-gain-db : audio gain selection for external analog modulation input.

	Valid values: 0 - 21, step by 3 (rounded down)

	Default: 0

Each led is represented as a sub-node of the issi,is31fl319x device.

There can be less leds subnodes than the chip can support but not more.

Required led sub-node properties:

- reg : number of LED line

	Valid values: 1 - number of leds supported by the chip variant.

Optional led sub-node properties:

- label : see Documentation/devicetree/bindings/leds/common.txt.

- linux,default-trigger :

	see Documentation/devicetree/bindings/leds/common.txt.

- led-max-microamp : (optional)

	Valid values: 5000 - 40000, step by 5000 (rounded down)

	Default: 20000 (20 mA)

	Note: a driver will take the lowest of all led limits since the

	chip has a single global setting. The lowest value will be chosen

	due to the PWM specificity, where lower brightness is achieved

	by reducing the dury-cycle of pulses and not the current, which

	will always have its peak value equal to led-max-microamp.

Examples:

fancy_leds: leds@65 {

	compatible = "issi,is31fl3196";

	#address-cells = <1>;

	#size-cells = <0>;

	reg = <0x65>;

	red_aux: led@1 {

		label = "red:aux";

		reg = <1>;

		led-max-microamp = <10000>;

	};

	green_power: led@5 {

		label = "green:power";

		reg = <5>;

		linux,default-trigger = "default-on";

	};

};