ARM i.MX51 babbage: Add display support

The babbage board has a DVI-I output which allows to output analog
and digital signals simultaneously. This patch adds support for it
to the devicetree. The DDC signals are not wired up on the board, so
DRM will fall back on default VESA modes.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Acked-by: Shawn Guo <shawn.guo@linaro.org>