arm64: dts: mediatek: mt7622: add missing "device_type" to memory nodes

arm64: dts: mediatek: mt7622: add missing "device_type" to memory nodes

This fixes:
arch/arm64/boot/dts/mediatek/mt7622-rfb1.dtb: /: memory@40000000: 'device_type' is a required property
        from schema $id: http://devicetree.org/schemas/memory.yaml#
arch/arm64/boot/dts/mediatek/mt7622-bananapi-bpi-r64.dtb: /: memory@40000000: 'device_type' is a required property
        from schema $id: http://devicetree.org/schemas/memory.yaml#

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Reviewed-by: Matthias Brugger <matthias.bgg@gmail.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20240122132357.31264-1-zajec5@gmail.com
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>