drm: bridge: add support for lontium LT9611UXC bridge

Add support for Lontium LT9611UXC HDMI bridge. Lontium LT9611UXC is a
DSI to HDMI bridge which supports two DSI ports and I2S port as an input
and HDMI port as output. Despite name being similar to LT9611, these
devices are different enough to warrant separate driver.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20201102011435.1100930-3-dmitry.baryshkov@linaro.org