omapfb: Add support for the OMAP3 Beagle DVI output

The default resolution is 1024x768@24bit

This version addresses the comments from Felipe Balbi adn Arun Edarath

Fixed-by: Felipe Contreras <felipe.contreras@gmail.com>
Fixed-by: Steve Sakoman <steve@sakoman.com>
Fixed-by: Jarkko Nikula <jarkko.nikula@gmail.com>
Fixed-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Koen Kooi <koen@openembedded.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Imre Deak <imre.deak@nokia.com>