Add initial Intel MID watchdog driver support.

This driver is an initial implementation of generic Intel MID watchdog
driver. Currently it supports Intel Merrifield platform.
Signed-off-by: Eric Ernst <eric.ernst@intel.com>
Signed-off-by: David Cohen <david.a.cohen@linux.intel.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>