arm64: dts: ti: k3-am62-wakeup: Introduce RTC node

Introduce digital RTC node in wakeup domain. Even though this has
no specific battery backup supply, this on-chip RTC is used in
cost-optimized board designs as a wakeup source.

Reviewed-by: Dhruva Gole <d-gole@ti.com>
Reviewed-by: Bryan Brattlof <bb@ti.com>
Link: https://lore.kernel.org/r/20230320165123.80561-2-nm@ti.com


Signed-off-by: Nishanth Menon <nm@ti.com>