arm64: dts: renesas: r9a09g087: Add ETHSS node

arm64: dts: renesas: r9a09g087: Add ETHSS node

Add an Ethernet Switch Subsystem (ETHSS) device node to the RZ/N2H
(R9A09G087) SoC. The ETHSS IP block is responsible for handling MII
pass-through or conversion to RMII/RGMII.

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://patch.msgid.link/20251028175458.1037397-3-prabhakar.mahadev-lad.rj@bp.renesas.com
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>