ARM: dts: am335x-bone-common: Enable PRU-ICSS node

ARM: dts: am335x-bone-common: Enable PRU-ICSS node

The PRU-ICSS target module node was left in disabled state in the base
am33xx-l4.dtsi file. Enable this node on all the AM335x beaglebone
boards as they mostly use a AM3358 or a AM3359 SoC which do contain
the PRU-ICSS IP. The PRUSS node and most of its child nodes are already
enabled in the base dts file, and so become effective automatically
with the enabling of this PRU-ICSS target-module node.

The corresponding PRU nodes can be disabled later on if there are
no use-cases defined to use a particular PRU core or the whole
PRU-ICSS subsystem itself if both its PRU cores are unused.

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