soc: ti: pruss: Enable support for ICSSG subsystems on K3 AM65x SoCs

The K3 AM65x family of SoCs have the next generation of the PRU-ICSS
processor subsystem capable of supporting Gigabit Ethernet, and is
commonly referred to as ICSSG. These SoCs contain typically three
ICSSG instances named ICSSG0, ICSSG1 and ICSSG2. The three ICSSGs are
identical to each other for the most part with minor SoC integration
differences and capabilities. The ICSSG2 supports slightly enhanced
features like SGMII mode Ethernet, while the ICSS0 and ICSSG1 instances
are limited to MII mode only.

The ICSSGs on K3 AM65x SoCs are in general super-sets of the PRUSS on the
AM57xx/66AK2G SoCs. They include two additional auxiliary PRU cores called
RTUs and few other additional sub-modules. The interrupt integration is
also different on the K3 AM65x SoCs and are propagated through various
SoC-level Interrupt Router and Interrupt Aggregator blocks. Other IP level
differences include different constant tables, differences in system event
interrupt input sources etc. They also do not have a programmable module
reset line like those present on AM33xx/AM43xx SoCs. The modules are reset
just like any other IP with the SoC's global cold/warm resets.

The existing pruss platform driver has been updated to support these new
ICSSG instances through new AM65x specific compatibles. A build dependency
with ARCH_K3 is added to enable building all the existing PRUSS platform
drivers for this ARMv8 platform.

Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Grzegorz Jaszczyk <grzegorz.jaszczyk@linaro.org>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>