media: mediatek: vcodec: Add mt8188 encoder driver

Add mt8188's compatible "mediatek,mt8188-vcodec-enc".
Add mt8188's device private data "mt8188_pdata".

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