Hisilicon Hip04 Soc NAND controller DT binding

Required properties:

- compatible:          Should be "hisilicon,504-nfc".
- reg:                 The first contains base physical address and size of
                       NAND controller's registers. The second contains base
                       physical address and size of NAND controller's buffer.
- interrupts:          Interrupt number for nfc.
- nand-bus-width:      See nand-controller.yaml.
- nand-ecc-mode:       Support none and hw ecc mode.
- #address-cells:      Partition address, should be set 1.
- #size-cells:         Partition size, should be set 1.

Optional properties:

- nand-ecc-strength:   Number of bits to correct per ECC step.
- nand-ecc-step-size:  Number of data bytes covered by a single ECC step.

The following ECC strength and step size are currently supported:

 - nand-ecc-strength = <16>, nand-ecc-step-size = <1024>

Flash chip may optionally contain additional sub-nodes describing partitions of
the address space. See mtd.yaml for more detail.

Example:

	nand: nand@4020000 {
		compatible = "hisilicon,504-nfc";
		reg = <0x4020000 0x10000>, <0x5000000 0x1000>;
		interrupts = <0 379 4>;
		nand-bus-width = <8>;
		nand-ecc-mode = "hw";
		nand-ecc-strength = <16>;
		nand-ecc-step-size = <1024>;
		#address-cells = <1>;
		#size-cells = <1>;

		partition@0 {
			label = "nand_text";
			reg = <0x00000000 0x00400000>;
		};

		...

	};
