Freescale's NAND flash controller (NFC)

This variant of the Freescale NAND flash controller (NFC) can be found on
Vybrid (vf610), MPC5125, MCF54418 and Kinetis K70.

Required properties:
- compatible: Should be set to "fsl,vf610-nfc".
- reg: address range of the NFC.
- interrupts: interrupt of the NFC.
- #address-cells: shall be set to 1. Encode the nand CS.
- #size-cells : shall be set to 0.
- assigned-clocks: main clock from the SoC, for Vybrid <&clks VF610_CLK_NFC>;
- assigned-clock-rates: The NAND bus timing is derived from this clock
    rate and should not exceed maximum timing for any NAND memory chip
    in a board stuffing. Typical NAND memory timings derived from this
    clock are found in the SoC hardware reference manual. Furthermore,
    there might be restrictions on maximum rates when using hardware ECC.

- #address-cells, #size-cells : Must be present if the device has sub-nodes
  representing partitions.

Required children nodes:
Children nodes represent the available nand chips. Currently the driver can
only handle one NAND chip.

Required properties:
- compatible: Should be set to "fsl,vf610-nfc-cs".
- nand-bus-width: see nand-controller.yaml
- nand-ecc-mode: see nand-controller.yaml

Required properties for hardware ECC:
- nand-ecc-strength: supported strengths are 24 and 32 bit (see nand-controller.yaml)
- nand-ecc-step-size: step size equals page size, currently only 2k pages are
    supported
- nand-on-flash-bbt: see nand-controller.yaml

Example:

	nfc: nand@400e0000 {
		compatible = "fsl,vf610-nfc";
		#address-cells = <1>;
		#size-cells = <0>;
		reg = <0x400e0000 0x4000>;
		interrupts = <GIC_SPI 83 IRQ_TYPE_LEVEL_HIGH>;
		clocks = <&clks VF610_CLK_NFC>;
		clock-names = "nfc";
		assigned-clocks = <&clks VF610_CLK_NFC>;
		assigned-clock-rates = <33000000>;

		nand@0 {
			compatible = "fsl,vf610-nfc-nandcs";
			reg = <0>;
			nand-bus-width = <8>;
			nand-ecc-mode = "hw";
			nand-ecc-strength = <32>;
			nand-ecc-step-size = <2048>;
			nand-on-flash-bbt;
		};
	};
