Holtek ht16k33 RAM mapping 16*8 LED controller driver with keyscan
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Required properties:
- compatible:		"holtek,ht16k33"
- reg:			I2C slave address of the chip.
- interrupt-parent:	A phandle pointing to the interrupt controller
			serving the interrupt for this chip.
- interrupts:		Interrupt specification for the key pressed interrupt.
- refresh-rate-hz:	Display update interval in HZ.
- debounce-delay-ms:	Debouncing interval time in milliseconds.
- linux,keymap: 	The keymap for keys as described in the binding
			document (devicetree/bindings/input/matrix-keymap.txt).

Optional properties:
- linux,no-autorepeat:	Disable keyrepeat.
- default-brightness-level: Initial brightness level [0-15] (default: 15).

Example:

&i2c1 {
	ht16k33: ht16k33@70 {
		compatible = "holtek,ht16k33";
		reg = <0x70>;
		refresh-rate-hz = <20>;
		debounce-delay-ms = <50>;
		interrupt-parent = <&gpio4>;
		interrupts = <5 (IRQ_TYPE_LEVEL_HIGH | IRQ_TYPE_EDGE_RISING)>;
		linux,keymap = <
			MATRIX_KEY(2, 0, KEY_F6)
			MATRIX_KEY(3, 0, KEY_F8)
			MATRIX_KEY(4, 0, KEY_F10)
			MATRIX_KEY(5, 0, KEY_F4)
			MATRIX_KEY(6, 0, KEY_F2)
			MATRIX_KEY(2, 1, KEY_F5)
			MATRIX_KEY(3, 1, KEY_F7)
			MATRIX_KEY(4, 1, KEY_F9)
			MATRIX_KEY(5, 1, KEY_F3)
			MATRIX_KEY(6, 1, KEY_F1)
		>;
	};
};
