ARM: dts: dra7: Add PRU-ICSS interconnect target-module nodes

The AM57xx family of SoCs contains two identical PRU-ICSS instances
that have a very unique SYSC register. The IPs do not have any
PRCM reset lines unlike those on AM33xx/AM437x SoCs. Add the PRUSS
interconnect target-module nodes with all the required properties.

Each of the PRUSS devices themselves shall be added as child nodes
to the corresponding interconnect node in the future. The PRU-ICSS
instances are only available on AM57xx family of SoCs and are not
supported on DRA7xx family of SoCs in general, so the target module
nodes are added in a separate dtsi file. This new dtsi file is
included in all the AM57xx SoC dtsi files, so the nodes are
automatically inherited and enabled on all AM57xx boards.

Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>