watchdog: Kontron PLD watchdog timer driver

Add watchdog timer support for the on-board PLD found on some Kontron embedded
modules.

Signed-off-by: Kevin Strasser <kevin.strasser@linux.intel.com>
Signed-off-by: Michael Brunner <michael.brunner@kontron.com>
Acked-by: Guenter Roeck <linux@roeck-us.net>
Acked-by: Darren Hart <dvhart@linux.intel.com>