arch: arm: dts: k3-am68-sk-r5: Sync with J721s2 R5 file

arch: arm: dts: k3-am68-sk-r5: Sync with J721s2 R5 file

Currently AM68 SK boots with J721s2 R5 DTS and then later changes to
AM68 SK DT during runtime.

To split the support of J721s2 and AM68, sync AM68 R5 DT with J721s2 R5
DT as that contains some essential node changes for booting up AM68
using AM68 R5 DT.

secure_proxy_sa3 and secure_proxy_mcu node changes are required for
establishing contact with ROM and TIFS running on SMS M4 core,
respectively, and the addition of new power domain helps in holding A72
cluster in reset for configuration of firewalls.

Reviewed-by: Neha Malcom Francis <n-francis@ti.com>
Signed-off-by: Manorit Chawdhry <m-chawdhry@ti.com>