Get rid of the custom reboot notifier block registration and use the one
provided by the watchdog core.

Note that this watchdog used to stop unconditionnaly on SYS_HALT and
SYS_POWER_OFF. The core function now calls ops->stop on SYS_HALT and
SYS_DOWN. To prevent the watchdog from being stopped on reboot, the
"always-running" property must be set, otherwise it will now be stopped.
Signed-off-by: Damien Riegel <damien.riegel@savoirfairelinux.com>
Reviewed-by: Vivien Didelot <vivien.didelot@savoirlinux.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>