drm/bridge: Introduce LT8912B DSI to HDMI bridge

Lontium LT8912B is a DSI to HDMI bridge.

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Adrien Grassein <adrien.grassein@gmail.com>
Reviewed-by: Robert Foss <robert.foss@linaro.org>
Signed-off-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20210326121955.1266230-3-adrien.grassein@gmail.com