media: mediatek: vcodec: add decoder compatible to support mt8188

1: add mt8188's compatible name: mediatek,mt8188-vcodec-dec.
2: mt8188 is lat single core architecture, using mtk_lat_sig_core_pdata to
   initialize private data.
3: Getting mt8188's chip name according to decoder compatible name.

Signed-off-by: Yunfei Dong <yunfei.dong@mediatek.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>