mtd: nand: add sunxi NFC dt bindings doc

Allwinner NAND Flash Controller (NFC)

Required properties:

- compatible : "allwinner,sun4i-a10-nand".

- reg : shall contain registers location and length for data and reg.

- interrupts : shall define the nand controller interrupt.

- #address-cells: shall be set to 1. Encode the nand CS.

- #size-cells : shall be set to 0.

- clocks : shall reference nand controller clocks.

- clock-names : nand controller internal clock names. Shall contain :

    * "ahb" : AHB gating clock

    * "mod" : nand controller clock

Optional children nodes:

Children nodes represent the available nand chips.

Optional properties:

- allwinner,rb : shall contain the native Ready/Busy ids.

 or

- rb-gpios : shall contain the gpios used as R/B pins.

- nand-ecc-mode : one of the supported ECC modes ("hw", "hw_syndrome", "soft",

  "soft_bch" or "none")

see Documentation/devicetree/mtd/nand.txt for generic bindings.

Examples:

nfc: nand@01c03000 {

	compatible = "allwinner,sun4i-a10-nand";

	reg = <0x01c03000 0x1000>;

	interrupts = <0 37 1>;

	clocks = <&ahb_gates 13>, <&nand_clk>;

	clock-names = "ahb", "mod";

	#address-cells = <1>;

	#size-cells = <0>;

	pinctrl-names = "default";

	pinctrl-0 = <&nand_pins_a &nand_cs0_pins_a &nand_rb0_pins_a>;

	status = "okay";

	nand@0 {

		reg = <0>;

		allwinner,rb = <0>;

		nand-ecc-mode = "soft_bch";

	};

};