arm64: dts: set initial SR watchdog timeout to 60 seconds

Set initial Stingray watchdog timeout to 60 seconds

By the time when the userspace watchdog daemon is ready and taking control
over, the watchdog timeout will then be reset to what's configured in the
daemon.

Signed-off-by: Ray Jui <ray.jui@broadcom.com>
Reviewed-by: Vladimir Olovyannikov <vladimir.olovyannikov@broadcom.com>
Reviewed-by: Scott Branden <scott.branden@broadcom.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>