arm64: dts: ti: k3-am65-mcu: Add mcu_secproxy

arm64: dts: ti: k3-am65-mcu: Add mcu_secproxy

MCU domain has it's own secure proxy for communicating with ROM and
for R5 micro controller firmware operations. This is in addition to
the one in the main domain NAVSS subsystem that is used for general
purpose communication.

Describe the node for use with bootloaders and firmware that require
this communication path which uses interrupts to corresponding micro
controller interrupt controller. Mark the node as disabled since this
instance does not have interrupts routed to the main processor by
default for a complete description of the node.

Signed-off-by: Nishanth Menon <nm@ti.com>
Link: https://lore.kernel.org/r/20230530165900.47502-4-nm@ti.com
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>