arm: dts: k3-j721e-main: Add C66x DSP nodes

The J721E SoCs have two TMS320C66x DSP Core Subsystems (C66x CorePacs)
in the MAIN voltage domain, each with a C66x Fixed/Floating-Point DSP
Core, and 32 KB of L1P & L1D configurable SRAMs/Cache and an additional
288 KB of L2 configurable SRAM/Cache. These subsystems do not have
an MMU but contain a Region Address Translator (RAT) sub-module for
translating 32-bit processor addresses into larger bus addresses.
The inter-processor communication between the main A72 cores and
these processors is achieved through shared memory and Mailboxes.
Add the DT nodes for these DSP processor sub-systems in the common
k3-j721e-main.dtsi file.

Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>