dt-bindings: arm64: dts: mediatek: Add rev4 of spherion

Add binding for newer version of Google Spherion (Acer Chromebook 514):
rev4.

Signed-off-by: Nícolas F. R. A. Prado <nfraprado@collabora.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20230721201705.387426-3-nfraprado@collabora.com


Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>