arm64: dts: mediatek: Add Acelink EW-7886CAX

Acelink EW-7886CAX is an MT7986A (AKA Filogic 830) based access point.
It has 512 MiB of RAM, one 2.5 Gbps PoE (802.3at) Ethernet port and
on-SoC Wi-Fi.

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20231207080512.3688-3-zajec5@gmail.com
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>