hwmon/sch56xx: Depend on watchdog for watchdog core functions

Since the watchdog code in sch56xx-common now uses the watchdog core, the
Kconfig entires for the sch5627 and sch5636 should depend on WATCHDOG
being set. Also select the watchdog core when we select one of the drivers.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>