CFI or JEDEC memory-mapped NOR flash

Flash chips (Memory Technology Devices) are often used for solid state
file systems on embedded devices.

 - compatible : should contain the specific model of flash chip(s)
   used, if known, followed by either "cfi-flash" or "jedec-flash"
 - reg : Address range(s) of the flash chip(s)
   It's possible to (optionally) define multiple "reg" tuples so that
   non-identical NOR chips can be described in one flash node.
 - bank-width : Width (in bytes) of the flash bank.  Equal to the
   device width times the number of interleaved chips.
 - device-width : (optional) Width of a single flash chip.  If
   omitted, assumed to be equal to 'bank-width'.
 - #address-cells, #size-cells : Must be present if the flash has
   sub-nodes representing partitions (see below).  In this case
   both #address-cells and #size-cells must be equal to 1.

For JEDEC compatible devices, the following additional properties
are defined:

 - vendor-id : Contains the flash chip's vendor id (1 byte).
 - device-id : Contains the flash chip's device id (1 byte).

In addition to the information on the flash bank itself, the
device tree may optionally contain additional information
describing partitions of the flash address space.  This can be
used on platforms which have strong conventions about which
portions of the flash are used for what purposes, but which don't
use an on-flash partition table such as RedBoot.

Each partition is represented as a sub-node of the flash device.
Each node's name represents the name of the corresponding
partition of the flash device.

Flash partitions
 - reg : The partition's offset and size within the flash bank.
 - label : (optional) The label / name for this flash partition.
   If omitted, the label is taken from the node name (excluding
   the unit address).
 - read-only : (optional) This parameter, if present, is a hint to
   Linux that this flash partition should only be mounted
   read-only.  This is usually used for flash partitions
   containing early-boot firmware images or data which should not
   be clobbered.

Example:

	flash@ff000000 {
		compatible = "amd,am29lv128ml", "cfi-flash";
		reg = <ff000000 01000000>;
		bank-width = <4>;
		device-width = <1>;
		#address-cells = <1>;
		#size-cells = <1>;
		fs@0 {
			label = "fs";
			reg = <0 f80000>;
		};
		firmware@f80000 {
			label ="firmware";
			reg = <f80000 80000>;
			read-only;
		};
	};

Here an example with multiple "reg" tuples:

	flash@f0000000,0 {
		#address-cells = <1>;
		#size-cells = <1>;
		compatible = "intel,PC48F4400P0VB", "cfi-flash";
		reg = <0 0x00000000 0x02000000
		       0 0x02000000 0x02000000>;
		bank-width = <2>;
		partition@0 {
			label = "test-part1";
			reg = <0 0x04000000>;
		};
	};
