drm/mediatek: dsi: Fine tune the line time caused by EOTp

Enabling EoTp will make the line time larger, so the hfp and
hbp should be reduced to keep line time.

Signed-off-by: Jitao Shi <jitao.shi@mediatek.com>
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>