arm: dts: mt8189: Add ethernet support for Genio 520/720 boards

arm: dts: mt8189: Add ethernet support for Genio 520/720 boards

Add Ethernet support for MediaTek MT8189-based Genio 520 and Genio 720
development boards.

The ethernet interface is disabled by default in the SoC dtsi and
enabled in the board-specific configuration with proper PHY settings.

The ethernet related nodes are not part of current dt submission on the
kernel [1] and come from downstream u-boot. When switching to
OF_UPSTREAM we should add them back.

[1]: https://lore.kernel.org/all/20251203-add-mediatek-genio-520-720-evk-v1-3-df794b2a30ae@collabora.com/

Signed-off-by: Julien Stephan <jstephan@baylibre.com>
Reviewed-by: Macpaul Lin <macpaul.lin@mediatek.com>
Link: https://patch.msgid.link/20260429-add-ethernet-support-for-genio-520-720-v4-8-be54e17239b7@baylibre.com
Signed-off-by: David Lechner <dlechner@baylibre.com>