V4L/DVB: uvc: Move constants and structures definitions to linux/usb/video.h

The UVC host and gadget drivers both define constants and structures in
private header files. Move all those definitions to linux/usb/video.h
where they can be shared by the two drivers (and be available for
userspace applications).

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>