arm64: dts: ti: var-som-am62p: Refactor IPC configuration into common dtsi

arm64: dts: ti: var-som-am62p: Refactor IPC configuration into common dtsi

Update the VAR-SOM-AM62P dtsi to align with the refactor introduced by
k3-am62p-ti-ipc-firmware.dtsi common file, allowing to remove the IPC
nodes from the board file including the new common dtsi.

No functional changes intended.

Signed-off-by: Stefano Radaelli <stefano.radaelli21@gmail.com>
Link: https://patch.msgid.link/20251003125031.30539-2-stefano.radaelli21@gmail.com
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>