drm/mediatek: Add ovl_adaptor support for MT8195

Add ovl_adaptor driver for MT8195.
Ovl_adaptor is an encapsulated module and designed for simplified
DRM control flow. This module is composed of 8 RDMAs, 4 MERGEs and
an ETHDR. Two RDMAs merge into one layer, so this module support 4
layers.

Signed-off-by: Nancy.Lin <nancy.lin@mediatek.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Tested-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Tested-by: Bo-Chen Chen <rex-bc.chen@mediatek.com>
Link: https://patchwork.kernel.org/project/linux-mediatek/patch/20230321121859.2355-4-nancy.lin@mediatek.com/


Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>