arm64: dts: ti: am642-phyboard-electra: Add PRU-ICSSG nodes

The phyBOARD-Electra implements two Ethernet ports utilizing PRUs.
Add configuration for both mac ports & PHYs.

Signed-off-by: Wadim Egorov <w.egorov@phytec.de>
Link: https://lore.kernel.org/r/20240815113212.3720403-1-w.egorov@phytec.de


Signed-off-by: Nishanth Menon <nm@ti.com>