ARM: dts: omap4-droid4: Add HDMI support

We can get HDMI working as long as the 5V regulator is on. There is
probably an encoder chip there too, but so far no idea what it might be.
Let's keep the 5V HDMI regulator always enabled for now as otherwise we
cannot detect the monitor properly.

Cc: devicetree@vger.kernel.org
Cc: Marcel Partap <mpartap@gmx.net>
Cc: Michael Scott <michael.scott@linaro.org>
Cc: Tomi Valkeinen <tomi.valkeinen@ti.com>
Tested-By: Sebastian Reichel <sre@kernel.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>