watchdog: davinci: add "timeout-sec" property

Since Davinci WDT has been switched to use WDT core, it became able
to support timeout-sec property, so add it to it's binding description.

Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@ti.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>

Documentation/devicetree/bindings/watchdog/davinci-wdt.txt

@@ -4,9 +4,13 @@ Required properties:
 - compatible : Should be "ti,davinci-wdt"
 - reg : Should contain WDT registers location and length
 
+Optional properties:
+- timeout-sec : Contains the watchdog timeout in seconds
+
 Examples:
 
 wdt: wdt@2320000 {
 	compatible = "ti,davinci-wdt";
 	reg = <0x02320000 0x80>;
+	timeout-sec = <30>;
 };