drm: bridge/dw_hdmi: add dw hdmi i2c bus adapter support

The change adds support of internal HDMI I2C master controller, this
subdevice is used by default, if "ddc-i2c-bus" DT property is omitted.

The main purpose of this functionality is to support reading EDID from
an HDMI monitor on boards, which don't have an I2C bus connected to
DDC pins.

The current implementation does not support "I2C Master Interface
Extended Read Mode" to read data addressed by non-zero segment
pointer, this means that if EDID has more than 1 extension blocks,
EDID reading operation won't succeed, in my practice all tested HDMI
monitors have at maximum one extension block.

Signed-off-by: Vladimir Zapolskiy <vladimir_zapolskiy@mentor.com>
Acked-by: Rob Herring <robh@kernel.org>
Tested-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>