arm64: dts: ti: k3-j721s2-ti-ipc-firmware: Refactor IPC cfg into new dtsi

arm64: dts: ti: k3-j721s2-ti-ipc-firmware: Refactor IPC cfg into new dtsi

The TI K3 J721S2 SoCs have multiple programmable remote processors like
R5F, C7x etc. The TI SDKs for J721S2 SoCs offer sample firmwares which
could be run on these cores to demonstrate an "echo" IPC test. Those
firmware require certain memory carveouts to be reserved from system
memory, timers to be reserved, and certain mailbox configurations for
interrupt based messaging. These configurations could be different for a
different firmware.

While DT is not meant for system configurations, at least refactor these
configurations from board level DTS into a dtsi for now. This dtsi for
TI IPC firmware is board-independent and can be applied to all boards
from the same SoC Family. This gets rid of code duplication and allows
more freedom for users developing custom firmware (or no firmware) to
utilize system resources better; easily by swapping out this dtsi. To
maintain backward compatibility, the dtsi is included in all boards.

Signed-off-by: Beleswar Padhi <b-padhi@ti.com>
Link: https://patch.msgid.link/20250908142826.1828676-27-b-padhi@ti.com
Signed-off-by: Nishanth Menon <nm@ti.com>