drm/mediatek: move mipi_dsi_host_register to probe

DSI panel driver need attach function which is include in
mipi_dsi_host_ops.

If mipi_dsi_host_register is not in probe, dsi panel will
probe more delay.

So move the mipi_dsi_host_register to probe from bind.

Signed-off-by: Jitao Shi <jitao.shi@mediatek.com>
Signed-off-by: CK Hu <ck.hu@mediatek.com>