arm64: dts: ti: k3-am64-main: Reserve OCMRAM for DMSC-lite and secure proxy communication

The final 128KB in SRAM is reserved by default for DMSC-lite code and
secure proxy communication buffer. The memory region used for DMSC-lite
code can be optionally freed up by secure firmware API[1]. However, the
buffer for secure proxy communication is not configurable. This default
hardware configuration is unique for AM64.

Therefore, indicate the area reserved for DMSC-lite code and secure proxy
communication buffer in the oc_sram device tree node.

[1] - http://downloads.ti.com/tisci/esd/latest/6_topic_user_guides/security_handover.html#triggering-security-handover



Signed-off-by: Aswath Govindraju <a-govindraju@ti.com>
Reviewed-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Nishanth Menon <nm@ti.com>
Link: https://lore.kernel.org/r/20210616171224.24635-3-a-govindraju@ti.com