arm: dts: k3-j7200-mcu: Add MCU domain R5F cluster node

arm: dts: k3-j7200-mcu: Add MCU domain R5F cluster node

The J7200 SoCs have 2 dual-core Arm Cortex-R5F processor (R5FSS)
subsystems/clusters. One R5F cluster is present within the MCU
domain (MCU_R5FSS0), and the other one is present within the MAIN
domain (MAIN_R5FSS0). Each of these can be configured at boot time
to be either run in a LockStep mode or in an Asymmetric Multi
Processing (AMP) fashion in Split-mode. These subsystems have 64 KB
each Tightly-Coupled Memory (TCM) internal memories for each core
split between two banks - ATCM and BTCM (further interleaved into
two banks). The TCMs of both Cores are combined in LockStep-mode
to provide a larger 128 KB of memory.

Add the DT node for the MCU domain R5F cluster/subsystem, the two
R5F cores are added as child nodes to the main cluster/subsystem node.
The cluster is configured to run in LockStep mode by default, with
the ATCMs enabled to allow the R5 cores to execute code from DDR with
boot-strapping code from ATCM. The inter-processor communication
between the main A72 cores and these processors is achieved through
shared memory and Mailboxes.

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