drm/omap: Remove the video/omapdss.h and move it's content to local header file

Move the contents of the video/omapdss.h header file to omapdrm/dss local
header file and remove the original global header. The omapfb stach is
using video/omapfb_dss.h so this change will complete the separation of the
two driver implementation.
Signed-off-by: NPeter Ujfalusi <peter.ujfalusi@ti.com>