ARM: dts: overo: Add support for DVI output

Summit and Tobi expansion boards have a HDMI connector with a TFP410
encoder. Add a common include file for this configuration, and then
use it for Summit and Tobi.

Signed-off-by: Florian Vaussard <florian.vaussard@epfl.ch>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Acked-by: Tony Lindgren <tony@atomide.com>