OMAP: board-generic: enable DSS for panda & sdp boards

Call the non-DT omapdss setup code from board-generic if the board is
omap4-panda or omap4-sdp. This will give us working omapdss for those
boards when using DT kernel.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>