drm/bridge: Add ti-tfp410 DVI transmitter driver

Add very basic ti-tfp410 DVI transmitter driver. The only feature
separating this from a completely dummy bridge is the EDID read
support trough DDC I2C. Even that functionality should be in a
separate generic connector driver. However, because of missing DRM
infrastructure support the connector is implemented within the bridge
driver. Some tfp410 HW specific features may be added later if needed,
because there is a set of registers behind i2c if it is connected.

This implementation is tested against my new tilcdc bridge support
and it works with BeagleBone DVI-D Cape Rev A3. A DT binding document
is also updated.

Signed-off-by: Jyri Sarha <jsarha@ti.com>
Acked-by: Rob Herring <robh@kernel.org>