omapfb: take omapfb's private omapdss into use

omapfb's private copy of omapdss is now ready to be used.

This patch makes omapfb use its private omapdss and display drivers, and
also makes omap_vout (which uses omapfb) to depend on omapfb.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Acked-by: Dave Airlie <airlied@gmail.com>
Acked-by: Rob Clark <robdclark@gmail.com>