arm64: dts: mediatek: Add OpenWrt One

arm64: dts: mediatek: Add OpenWrt One

OpenWrt One is the first ever OpenWrt product. It's based on MT7981B
(AKA Filogic 820) and has 1 GiB or DDR4 RAM. The rest of peripherals
remains to be added later.

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20240527115933.7396-4-zajec5@gmail.com
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>