This lets the serial gadget work with another controller.

Tell serial about omap_udc.  This driver still needs updating to
use the endpoint autoconfig suppport; like Gadget Zero, it
really shouldn't need _any_ hardware-specific #ifdeffery.
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>