dt-bindings: watchdog: Add optional 'timeout-sec' property for sp805

Update the SP805 binding document to add optional 'timeout-sec'
devicetree property

Signed-off-by: Ray Jui <ray.jui@broadcom.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>

Documentation/devicetree/bindings/watchdog/arm,sp805.txt

@@ -19,6 +19,8 @@ Required properties:
 
 Optional properties:
 - interrupts:  Should specify WDT interrupt number
+- timeout-sec: Should specify default WDT timeout in seconds. If unset, the
+               default timeout is determined by the driver
 
 Example:
 	watchdog@66090000 {