drivers/video: remove unused parameter in Kconfig

This patch proposes to remove the FB_NUC900_DEBUG kernel configuration
parameter defined in drivers/video/Kconfig, but used nowhere
in the makefiles and source code.

Signed-off-by: Michael Opdenacker <michael.opdenacker@free-electrons.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>