dt-bindings: arm64: mediatek: Add MT7981B and Xiaomi AX3000T

MT7981B (AKA Filogic 820) is MediaTek's dual-core ARM Cortex-A53 SoC.
One of market devices using this SoC is Xiaomi AX3000T.

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20240111103928.721-2-zajec5@gmail.com


Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>