dt-bindings: watchdog: Add bindings for RAVE SP watchdog driver

Add Device Tree bindings for RAVE SP watchdog drvier - an MFD cell of
parent RAVE SP driver (documented in
Documentation/devicetree/bindings/mfd/zii,rave-sp.txt).
Acked-by: Philippe Ombredanne <pombredanne@nexb.com>
Acked-by: Pavel Machek <pavel@ucw.cz>
Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Nikita Yushchenko <nikita.yoush@cogentembedded.com>
Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

Documentation/devicetree/bindings/watchdog/zii,rave-sp-wdt.txt

+Zodiac Inflight Innovations RAVE Supervisory Processor Watchdog Bindings
+
+RAVE SP watchdog device is a "MFD cell" device corresponding to
+watchdog functionality of 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: Depending on wire protocol implemented by RAVE SP
+  firmware, should be one of:
+	- "zii,rave-sp-watchdog"
+	- "zii,rave-sp-watchdog-legacy"
+
+Optional properties:
+
+- wdt-timeout:	Two byte nvmem cell specified as per
+		Documentation/devicetree/bindings/nvmem/nvmem.txt
+
+Example:
+
+	rave-sp {
+		compatible = "zii,rave-sp-rdu1";
+		current-speed = <38400>;
+
+		eeprom {
+			wdt_timeout: wdt-timeout@8E {
+				reg = <0x8E 2>;
+			};
+		};
+
+		watchdog {
+			compatible = "zii,rave-sp-watchdog";
+			nvmem-cells = <&wdt_timeout>;
+			nvmem-cell-names = "wdt-timeout";
+		};
+	}
+