dt-bindings: display: bridge: Add documentation for LT9611UXC

Lontium LT9611UXC is a DSI to HDMI bridge which supports 2 DSI ports
and I2S port as input and one HDMI port as output. The LT9611UXC chip is
handled by a separate driver, but the bindings used are fully compatible
with the LT9611 chip, so let's reuse the lt9611.yaml schema.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Acked-by: Vinod Koul <vkoul@kernel.org>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20201102011435.1100930-2-dmitry.baryshkov@linaro.org