arm64: dts: ti: k3-am642-sr-som: Add missing cfg for TI IPC Firmware

arm64: dts: ti: k3-am642-sr-som: Add missing cfg for TI IPC Firmware

Currently, only R5F remote processors are enabled for k3-am642-sr SoMs,
whereas the M4F in MCU domain is disabled. Enable the M4F remote
processor at board level by reserving memory carveouts and assigning
mailboxes.

While at it, reserve the MAIN domain timers that are used by R5F remote
processors for ticks to avoid rproc crashes. This config aligns with
other AM64 boards and can be refactored out later.

Signed-off-by: Beleswar Padhi <b-padhi@ti.com>
Link: https://patch.msgid.link/20250908142826.1828676-19-b-padhi@ti.com
Signed-off-by: Nishanth Menon <nm@ti.com>