Update kernel header files

Update videodev2.h and move it under include/linux. v4l2-common.h and
v4l2-controls.h are now required by videodev2.h as well --- they're really
the reason for moving videodev2.h. The two required headers are added, too.

Signed-off-by: Sakari Ailus <sakari.ailus@iki.fi>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Print v4l2_buffer timestamp type

Signed-off-by: Sakari Ailus <sakari.ailus@iki.fi>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>