drm/bridge: add Silicon Image SiI9234 driver

SiI9234 transmitter converts eTMDS/HDMI signal to MHL 1.0.
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.

This patch is based on the code refactored by Tomasz Stanislawski
<t.stanislaws@samsung.com>, which was initially developed by:
Adam Hampson <ahampson@sta.samsung.com>
Erik Gilling <konkers@android.com>
Shankar Bandal <shankar.b@samsung.com>
Dharam Kumar <dharam.kr@samsung.com>

Signed-off-by: Maciej Purski <m.purski@samsung.com>
Acked-by: Rob Herring <robh@kernel.org> [for dt bindings]
Reviewed-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1507212431-5801-2-git-send-email-m.purski@samsung.com