watchdog: dw: Enable OF support for DW watchdog timer

Add device tree support to the DW watchdog timer.

Signed-off-by: Dinh Nguyen <dinguyen@altera.com>
Acked-by: Jamie Iles <jamie@jamieiles.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Pavel Machek <pavel@denx.de>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>
Cc: Viresh Kumar <viresh.linux@gmail.com>
Cc: Rob Herring <rob.herring@calxeda.com>
Cc: Pawel Moll <pawel.moll@arm.com>
Cc: Stephen Warren <swarren@wwwdotorg.org>
Cc: Ian Campbell <ijc+devicetree@hellion.org.uk>
Cc: devicetree@vger.kernel.org
Cc: linux-watchdog@vger.kernel.org