OMAP: DSS2: Move panel-generic-dpi.h to include/video/

arch/arm/plat-omap/include/plat/panel-generic-dpi.h is an include for
the OMAP DSS panel driver for generic DPI displays. A more logical place
for it is in include/video.

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