dt-bindings: mtd: add tegra NAND controller binding

This adds the devicetree binding for the Tegra 2 NAND flash
controller.
Signed-off-by: NLucas Stach <dev@lynxeye.de>
Signed-off-by: NStefan Agner <stefan@agner.ch>
Reviewed-by: NBoris Brezillon <boris.brezillon@bootlin.com>
Reviewed-by: NRob Herring <robh@kernel.org>
Signed-off-by: NMiquel Raynal <miquel.raynal@bootlin.com>

Documentation/devicetree/bindings/mtd/nvidia-tegra20-nand.txt

+NVIDIA Tegra NAND Flash controller
+
+Required properties:
+- compatible: Must be one of:
+  - "nvidia,tegra20-nand"
+- reg: MMIO address range
+- interrupts: interrupt output of the NFC controller
+- clocks: Must contain an entry for each entry in clock-names.
+  See ../clocks/clock-bindings.txt for details.
+- clock-names: Must include the following entries:
+  - nand
+- resets: Must contain an entry for each entry in reset-names.
+  See ../reset/reset.txt for details.
+- reset-names: Must include the following entries:
+  - nand
+
+Optional children nodes:
+Individual NAND chips are children of the NAND controller node. Currently
+only one NAND chip supported.
+
+Required children node properties:
+- reg: An integer ranging from 1 to 6 representing the CS line to use.
+
+Optional children node properties:
+- nand-ecc-mode: String, operation mode of the NAND ecc mode. Currently only
+		 "hw" is supported.
+- nand-ecc-algo: string, algorithm of NAND ECC.
+		 Supported values with "hw" ECC mode are: "rs", "bch".
+- nand-bus-width : See nand.txt
+- nand-on-flash-bbt: See nand.txt
+- nand-ecc-strength: integer representing the number of bits to correct
+		     per ECC step (always 512). Supported strength using HW ECC
+		     modes are:
+		     - RS: 4, 6, 8
+		     - BCH: 4, 8, 14, 16
+- nand-ecc-maximize: See nand.txt
+- nand-is-boot-medium: Makes sure only ECC strengths supported by the boot ROM
+		       are chosen.
+- wp-gpios: GPIO specifier for the write protect pin.
+
+Optional child node of NAND chip nodes:
+Partitions: see partition.txt
+
+  Example:
+	nand-controller@70008000 {
+		compatible = "nvidia,tegra20-nand";
+		reg = <0x70008000 0x100>;
+		interrupts = <GIC_SPI 24 IRQ_TYPE_LEVEL_HIGH>;
+		clocks = <&tegra_car TEGRA20_CLK_NDFLASH>;
+		clock-names = "nand";
+		resets = <&tegra_car 13>;
+		reset-names = "nand";
+
+		nand@0 {
+			reg = <0>;
+			#address-cells = <1>;
+			#size-cells = <1>;
+			nand-bus-width = <8>;
+			nand-on-flash-bbt;
+			nand-ecc-algo = "bch";
+			nand-ecc-strength = <8>;
+			wp-gpios = <&gpio TEGRA_GPIO(S, 0) GPIO_ACTIVE_LOW>;
+		};
+	};