x86: intel-mid: add watchdog platform code for Merrifield

This patch adds platform code for Intel Merrifield.
Since the watchdog is not part of SFI table, we have no other option but
to manually register watchdog's platform device (argh!).

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>