media: dt-bindings: mediatek,vcodec: Don't require assigned-clocks

On MT8183 it's not necessary to configure the parent for the clocks.
Remove the assigned-clocks and assigned-clock-parents from the required
list.

Signed-off-by: Nícolas F. R. A. Prado <nfraprado@collabora.com>
Reviewed-by: Matthias Brugger <matthias.bgg@gmail.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>