dt-bindings: nvmem: Add binding for RAVE SP EEPROM driver

Add Device Tree bindings for RAVE SP EEPROM driver - an MFD cell of
parent RAVE SP driver (documented in
Documentation/devicetree/bindings/mfd/zii,rave-sp.txt).

Cc: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Cc: linux-kernel@vger.kernel.org
Cc: Chris Healy <cphealy@gmail.com>
Cc: Lucas Stach <l.stach@pengutronix.de>
Cc: Aleksander Morgado <aleksander@aleksander.es>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: devicetree@vger.kernel.org
Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/nvmem/zii,rave-sp-eeprom.txt

+Zodiac Inflight Innovations RAVE EEPROM Bindings
+
+RAVE SP EEPROM device is a "MFD cell" device exposing physical EEPROM
+attached to RAVE Supervisory Processor. It is expected that its Device
+Tree node is specified as a child of the node corresponding to the
+parent RAVE SP device (as documented in
+Documentation/devicetree/bindings/mfd/zii,rave-sp.txt)
+
+Required properties:
+
+- compatible: Should be "zii,rave-sp-eeprom"
+
+Optional properties:
+
+- zii,eeprom-name: Unique EEPROM identifier describing its function in the
+  system. Will be used as created NVMEM deivce's name.
+
+Data cells:
+
+Data cells are child nodes of eerpom node, bindings for which are
+documented in Documentation/bindings/nvmem/nvmem.txt
+
+Example:
+
+	rave-sp {
+		compatible = "zii,rave-sp-rdu1";
+		current-speed = <38400>;
+
+		eeprom@a4 {
+			compatible = "zii,rave-sp-eeprom";
+			reg = <0xa4 0x4000>;
+			#address-cells = <1>;
+			#size-cells = <1>;
+			zii,eeprom-name = "main-eeprom";
+
+			wdt_timeout: wdt-timeout@81 {
+				reg = <0x81 2>;
+			};
+		};
+	}