[WATCHDOG] Add SMSC SCH311x Watchdog Timer.

Add a watchdog driver for the hardware watchdog timer on the
SMSC SCH3112, SCH3114 and SCH3116 Super IO chipset.

Tested-by: Marco Chiappero <marco@absence.it>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>