ARM: dts: AM4372: Add the PRU-ICSS1 DT node

ARM: dts: AM4372: Add the PRU-ICSS1 DT node

Add the DT node for the PRU-ICSS1 instance on the AM437x family
of SoCs. Each PRU-ICSS instance is represented by the pruss-soc-bus
node and a child PRUSS subsystem node. The PRU-ICSS instances are
not supported on AM4372 SoC though in the AM437x family, so the
nodes are added in disabled state in the common am4372 dtsi file.
They should be enabled in only those derivative board files that
use a SoC containing PRU-ICSS.

The PRU-ICSS1 on AM437x is very similar to the PRUSS in AM33xx,
except for variations in the RAM sizes, bus addresses and the
number of interrupts coming into the MPU INTC (host interrupt
7 is routed to the other PRUSS instead of MPU).

The PRUSS subsystem node contains the entire address space and
the various interrupts generated towards the main MPU. The various
sub-modules of the PRU-ICSS are represented as individual child
nodes (so platform devices themselves) of the PRUSS subsystem node.
These include the two PRU cores and the interrupt controller. The
Industrial Ethernet Peripheral (IEP), the Real Time Media Independent
Interface controller (MII_RT), and the CFG sub-module are represented
as syscon nodes. All the Data RAMs are represented within a child node
of its own named 'memories' without any compatible.

The DT nodes use all standard properties. The regs property in the
PRU nodes define the addresses for the Instruction RAM, the Debug
and Control sub-modules for that PRU core. The firmware for each
PRU core is defined through a 'firmware-name' property.

The default names for the firmware images for each PRU core are
defined as follows (these can be adjusted either in derivative
board dts files or through sysfs at runtime if required):
     PRU-ICSS1 PRU0 Core: am437x-pru1_0-fw
     PRU-ICSS1 PRU1 Core: am437x-pru1_1-fw

Signed-off-by: Suman Anna <s-anna@ti.com>