drm/mediatek: dpi: Add check for max clock rate in mode_valid

Add per-platform max clock rate check in mtk_dpi_bridge_mode_valid.

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