ARM: mvebu: Add A375/A380 watchdog binding documentation

This commit documents the new support for "marvell,armada-{375,380}-wdt"
compatible strings and the extra 'reg' entry requirement.

Signed-off-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Acked-by: Jason Cooper <jason@lakedaemon.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>

Documentation/devicetree/bindings/watchdog/marvel.txt

@@ -5,11 +5,18 @@ Required Properties:
 - Compatibility : "marvell,orion-wdt"
 		  "marvell,armada-370-wdt"
 		  "marvell,armada-xp-wdt"
+		  "marvell,armada-375-wdt"
+		  "marvell,armada-380-wdt"
 
 - reg		: Should contain two entries: first one with the
 		  timer control address, second one with the
 		  rstout enable address.
 
+For "marvell,armada-375-wdt" and "marvell,armada-380-wdt":
+
+- reg		: A third entry is mandatory and should contain the
+                  shared mask/unmask RSTOUT address.
+
 Optional properties:
 
 - interrupts	: Contains the IRQ for watchdog expiration