arm: dts: Add support for A72 specific J721S2 Common Processor Board

arm: dts: Add support for A72 specific J721S2 Common Processor Board

The EVM architecture for J721S2 is similar to that of J721E and J7200. It
is as follows,

+------------------------------------------------------+
|   +-------------------------------------------+      |
|   |                                           |      |
|   |        Add-on Card 1 Options              |      |
|   |                                           |      |
|   +-------------------------------------------+      |
|                                                      |
|                                                      |
|                     +-------------------+            |
|                     |                   |            |
|                     |   SOM             |            |
|  +--------------+   |                   |            |
|  |              |   |                   |            |
|  |  Add-on      |   +-------------------+            |
|  |  Card 2      |                                    |    Power Supply
|  |  Options     |                                    |    |
|  |              |                                    |    |
|  +--------------+                                    | <---
+------------------------------------------------------+
                                 Common Processor Board

Common Processor board is the baseboard that contains most of the actual
connectors, power supply etc. The System on Module (SoM) is plugged on to
the common processor baord. Therefore, add support for peripherals brought
out in the common processor board.

Link to Common Processor Board: https://www.ti.com/lit/zip/sprr439

Signed-off-by: Aswath Govindraju <a-govindraju@ti.com>