watchdog: add Intel MID watchdog driver support

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>