drm/bridge: lt9611: properly program the dual host mode

If the bridge is connected using both DSI ports, the driver should use
both of them all the time. Correct programming sequence to always use
dual-port mode if both dsi0 and dsi1 are connected.

Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230118081658.2198520-14-dmitry.baryshkov@linaro.org