[media] v4l: Move the media/v4l2-mediabus.h header to include/linux

The header defines the v4l2_mbus_framefmt structure which will be used
by the V4L2 subdevs userspace API.

Change the type of the v4l2_mbus_framefmt::code field to __u32, as enum
sizes can differ between different ABIs on the same architectures.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>