drm/bridge: add Silicon Image SiI8620 driver

SiI8620 transmitter converts eTMDS/HDMI signal to MHL 3.0.
It is controlled via I2C bus. Its interaction with other
devices in video pipeline is performed mainly on HW level.
The only interaction it does on device driver level is
filtering-out unsupported video modes, it exposes drm_bridge
interface to perform this operation.

Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Archit Taneja <architt@codeaurora.org>
Link: http://patchwork.freedesktop.org/patch/msgid/1476085157-5266-1-git-send-email-a.hajda@samsung.com