soc: ti: pruss: Add pruss_soc_bus platform driver

soc: ti: pruss: Add pruss_soc_bus platform driver

The Programmable Real-Time Unit - Industrial Communication
Subsystem (PRU-ICSS) is present of various TI SoCs such as
AM335x or AM437x or the Keystone 66AK2G. Each SoC can have
one or more PRUSS instances that may or may not be identical.
For example, AM335x SoCs have a single PRUSS, while AM437x has
two PRUSS instances PRUSS1 and PRUSS0, with the PRUSS0 being
a cut-down version of the PRUSS1.

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.

The PRU-ICSS functionality is achieved through four different
modules, each implementing a platform driver addressing a
specific portion of the PRUSS. Some sub-modules of the PRU-ICSS
IP reuse some of the existing drivers (like davinci mdio driver
or the generic syscon driver). The pruss_soc_bus driver deals
with the SoC integration aspects of the PRUSS IP(s) and manages
the common clock, reset and interconnect configuration and
creates the child PRUSS devices. The second pruss driver is
responsible for the creation and deletion of various platform
devices for the child PRU device and other child devices. A third
driver manages the PRUSS interrupt controller and implements an
irqchip driver to provide a Linux standard way of interrupt
management to PRU clients. The fourth platform driver is a
remoteproc driver and performs the individual PRU RISC cores
management. This design provides flexibility in representing
the different modules of PRUSS accordingly.

The driver currently supports the AM335x SoC, and support for
other TI SoCs will be added in subsequent patches.

Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Keerthy <j-keerthy@ti.com>
Signed-off-by: Roger Quadros <rogerq@ti.com>