drm/mediatek: dpi: Add bus format negotiation

Add the atomic_get_output_bus_fmts, atomic_get_input_bus_fmts to negotiate
the possible output and input formats for the current mode and monitor,
and use the negotiated formats in a basic atomic_check callback.

Signed-off-by: Jitao Shi <jitao.shi@mediatek.com>
Signed-off-by: Rex-BC Chen <rex-bc.chen@mediatek.com>
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>