realtek: Add and enable watchdog node

realtek: Add and enable watchdog node

Add and enable the Realtek Otto WDT peripheral found on these SoCs.

Default all devices to use standard (cold) reboot and "soc" resets.

Devices that require the PLL value fixup before restarting, should pick
the "cpu" or "software" reset mode. These devices also need to provide a
custom reboot mode, by adding the reboot argument to the kernel command
line:

    WDT reset mode  | kernel reboot mode
    ----------------+---------------------------------------
    soc             | reboot=cold (default if not specified)
    cpu             | reboot=warm
    software        | reboot=software

Preferrably, these devices should use an alternative restart method like
gpio-restart to provide reliable restarts.

Note that watchdog restarts are not yet exposed, since the
_machine_restart override is still present.

Signed-off-by: Sander Vanheule <sander@svanheule.net>
Tested-by: Stijn Segers <foss@volatilesystems.org>
Tested-by: Paul Fertser <fercerpav@gmail.com>
Tested-by: Stijn Tintel <stijn@linux-ipv6.be>