drm/bridge: Introduce LT9611 DSI to HDMI bridge

Lontium Lt9611 is a DSI to HDMI bridge which supports two DSI ports and
I2S port as an input and HDMI port as output

Co-developed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Co-developed-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Tested-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org> # fix lt9611_bridge_mode_valid
Link: https://patchwork.freedesktop.org/patch/msgid/20200723163442.1280414-4-vkoul@kernel.org