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

Documentation/devicetree/bindings/arm/mediatek.yaml

@@ -82,6 +82,10 @@ properties:
           - enum:
               - mediatek,mt7629-rfb
           - const: mediatek,mt7629
+      - items:
+          - enum:
+              - xiaomi,ax3000t
+          - const: mediatek,mt7981b
       - items:
           - enum:
               - bananapi,bpi-r3