media: dt-bindings: media: mediatek: vcodec: Add encoder dt-bindings for mt8188

Add encoder dt-bindings for mt8188.

Signed-off-by: Irui Wang <irui.wang@mediatek.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>