dt-bindings: media: mtk-vcodec-encoder: add compatible for mt8186

dt-bindings: media: mtk-vcodec-encoder: add compatible for mt8186

Add compatible for the mt8186 encoder which currently works in the same
way as mt8183.

Signed-off-by: Eugen Hristev <eugen.hristev@collabora.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20231228113245.174706-5-eugen.hristev@collabora.com
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>