Add the DT nodes for the ICSSG0, ICSSG1 and ICSSG2 processor subsystems
that are present on the K3 AM65x SoCs. The three ICSSGs are identical
to each other for the most part, with the ICSSG2 supporting slightly
enhanced features for supporting SGMII PRU Ethernet. Each ICSSG instance
is represented by a PRUSS subsystem node. These nodes are enabled by
default.

DT nodes are fetch from Linux 5.13 Kernel.
Signed-off-by: NLokesh Vutla <lokeshvutla@ti.com>
Link: https://lore.kernel.org/r/20210622063431.3151-5-lokeshvutla@ti.com