drm/mediatek: Add ovl_adaptor get format function

1. Add ovl_adaptor get_format and get_num_formats component function.
The two functions are needed for getting the supported format in
mtk_plane_init().
2. Get supported format from the ovl_adaptor's rdma engine - mdp_rdma.

Signed-off-by: Nancy.Lin <nancy.lin@mediatek.com>
Link: https://patchwork.kernel.org/project/linux-mediatek/patch/20230330032614.18837-3-nancy.lin@mediatek.com/


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