mtd: gpio-nand: add device tree bindings

Add device tree bindings so that the gpio-nand driver may be
instantiated from the device tree.  This also allows the partitions
to be specified in the device tree.

v7:	- restore runtime device tree/non device tree detection
v6:	- convert to mtd_device_parse_register()
v5:	- fold dt config helpers into a single gpio_nand_of_get_config()
v4:	- get io sync address from gpio-control-nand,io-sync-reg
	  property rather than a resource
	- clarified a few details in the binding
v3:	- remove redundant cast and a couple of whitespace/naming
	  changes
v2:	- add CONFIG_OF guards for non-dt platforms
	- compatible becomes gpio-control-nand
	- clarify some binding details

Signed-off-by: Jamie Iles <jamie@jamieiles.com>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

Documentation/devicetree/bindings/mtd/gpio-control-nand.txt

@@ -0,0 +1,44 @@
+GPIO assisted NAND flash
+
+The GPIO assisted NAND flash uses a memory mapped interface to
+read/write the NAND commands and data and GPIO pins for the control
+signals.
+
+Required properties:
+- compatible : "gpio-control-nand"
+- reg : should specify localbus chip select and size used for the chip.  The
+  resource describes the data bus connected to the NAND flash and all accesses
+  are made in native endianness.
+- #address-cells, #size-cells : Must be present if the device has sub-nodes
+  representing partitions.
+- gpios : specifies the gpio pins to control the NAND device.  nwp is an
+  optional gpio and may be set to 0 if not present.
+
+Optional properties:
+- bank-width : Width (in bytes) of the device.  If not present, the width
+  defaults to 1 byte.
+- chip-delay : chip dependent delay for transferring data from array to
+  read registers (tR).  If not present then a default of 20us is used.
+- gpio-control-nand,io-sync-reg : A 64-bit physical address for a read
+  location used to guard against bus reordering with regards to accesses to
+  the GPIO's and the NAND flash data bus.  If present, then after changing
+  GPIO state and before and after command byte writes, this register will be
+  read to ensure that the GPIO accesses have completed.
+
+Examples:
+
+gpio-nand@1,0 {
+	compatible = "gpio-control-nand";
+	reg = <1 0x0000 0x2>;
+	#address-cells = <1>;
+	#size-cells = <1>;
+	gpios = <&banka 1 0	/* rdy */
+		 &banka 2 0 	/* nce */
+		 &banka 3 0 	/* ale */
+		 &banka 4 0 	/* cle */
+		 0		/* nwp */>;
+
+	partition@0 {
+	...
+	};
+};