dt-bindings: remoteproc: mediatek: Add binding for mt8186 scp

Add mt8186 compatible to binding document.

Signed-off-by: Allen-KH Cheng <Allen-KH.Cheng@mediatek.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20220225132747.31808-2-allen-kh.cheng@mediatek.com