[WATCHDOG] mv64x60_wdt: Add a module parameter to change nowayout setting

Also, use the WATCHDOG_NOWAYOUT macro, rather than #ifdefs,
and use __module_get to prevent module unloading if WATCHDOG_NOWAYOUT
is set.

Signed-off-by: Dale Farnsworth <dale@farnsworth.org>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>