Common watchdog properties.

Optional properties:
- timeout-sec : Timeout of the watchdog in seconds
                If this timeout is not defined, the value of WATCHDOG_TIMEOUT_MSECS will
                be used instead.
- hw_margin_ms : Period used to reset the watchdog in ms
                 If this period is not defined, the default value is 1000.
- u-boot,noautostart :
- u-boot,autostart : These (mutually exclusive) boolean properties can be used to control
                     whether the watchdog is automatically started when probed. If neither
                     are present, the behaviour is determined by the config option
                     WATCHDOG_AUTOSTART.
