Add the DT entry for a watchdog based on RTI1.

On SR1.0 silicon, it requires additional firmware on the MCU R5F cores
to handle the expiry, e.g. https://github.com/siemens/k3-rti-wdt. As
this firmware will also lock the power domain to protect it against
premature shutdown, mark it shared.
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Nishanth Menon <nm@ti.com>
Acked-by: Praneeth Bajjuri <praneeth@ti.com>
Link: https://lore.kernel.org/r/279c20fa-6e5e-4f88-9cd1-f76297a28a19@web.de