drm/mediatek: Add ETHDR support for MT8195

ETHDR is a part of ovl_adaptor.
ETHDR is designed for HDR video and graphics conversion in the external
display path. It handles multiple HDR input types and performs tone
mapping, color space/color format conversion, and then combine
different layers, output the required HDR or SDR signal to the
subsequent display path.

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/20230321121859.2355-3-nancy.lin@mediatek.com/
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>