soc: ti: pruss: Add a platform driver for PRUSS in TI SoCs

The Programmable Real-Time Unit - Industrial Communication
Subsystem (PRU-ICSS) is present of various TI SoCs such as
AM335x or AM437x or the AM654x family. Each SoC can have
one or more PRUSS instances that may or may not be identical.

The PRUSS consists of dual 32-bit RISC cores called the
Programmable Real-Time Units (PRUs), some shared, data and
instruction memories, some internal peripheral modules, and
an interrupt controller. The programmable nature of the PRUs
provide flexibility to implement custom peripheral interfaces,
fast real-time responses, or specialized data handling.

Add support for pruss driver. Currently am654x family
is supported.

Signed-off-by: Keerthy <j-keerthy@ti.com>
Signed-off-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
Link: https://lore.kernel.org/r/20210622063431.3151-2-lokeshvutla@ti.com