* NAND chip and NAND controller generic binding

NAND controller/NAND chip representation:

The NAND controller should be represented with its own DT node, and all
NAND chips attached to this controller should be defined as children nodes
of the NAND controller. This representation should be enforced even for
simple controllers supporting only one chip.

Mandatory NAND controller properties:
- #address-cells: depends on your controller. Should at least be 1 to
		  encode the CS line id.
- #size-cells: depends on your controller. Put zero unless you need a
	       mapping between CS lines and dedicated memory regions

Optional NAND controller properties
- ranges: only needed if you need to define a mapping between CS lines and
	  memory regions

Optional NAND chip properties:

- nand-ecc-mode : String, operation mode of the NAND ecc mode.
		  Supported values are: "none", "soft", "hw", "hw_syndrome",
		  "hw_oob_first", "on-die".
		  Deprecated values:
		  "soft_bch": use "soft" and nand-ecc-algo instead
- nand-ecc-algo: string, algorithm of NAND ECC.
		 Valid values are: "hamming", "bch", "rs".
- nand-bus-width : 8 or 16 bus width if not present 8
- nand-on-flash-bbt: boolean to enable on flash bbt option if not present false

- nand-ecc-strength: integer representing the number of bits to correct
		     per ECC step.

- nand-ecc-step-size: integer representing the number of data bytes
		      that are covered by a single ECC step.

- nand-ecc-maximize: boolean used to specify that you want to maximize ECC
		     strength. The maximum ECC strength is both controller and
		     chip dependent. The controller side has to select the ECC
		     config providing the best strength and taking the OOB area
		     size constraint into account.
		     This is particularly useful when only the in-band area is
		     used by the upper layers, and you want to make your NAND
		     as reliable as possible.
- nand-is-boot-medium: Whether the NAND chip is a boot medium. Drivers might use
		       this information to select ECC algorithms supported by
		       the boot ROM or similar restrictions.

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

The ECC strength and ECC step size properties define the correction capability
of a controller. Together, they say a controller can correct "{strength} bit
errors per {size} bytes".

The interpretation of these parameters is implementation-defined, so not all
implementations must support all possible combinations. However, implementations
are encouraged to further specify the value(s) they support.

Example:

	nand-controller {
		#address-cells = <1>;
		#size-cells = <0>;

		/* controller specific properties */

		nand@0 {
			reg = <0>;
			nand-ecc-mode = "soft";
			nand-ecc-algo = "bch";

			/* controller specific properties */
		};
	};
