OMAP: DSS2: remove extra includes from include/video/omapdss.h

omapdss.h included platform_device.h and atomic.h, neither of which is
needed by omapdss.h. Remove those includes from omapdss.h, and fix the
affected .c files which did not include platform_device.h even though
they should.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>