[media] vivid: add some missing headers

That remove a few warnings:

drivers/media/platform/vivid/vivid-kthread-out.c:226:5: warning: no previous prototype for 'vivid_start_generating_vid_out' [-Wmissing-prototypes]
 int vivid_start_generating_vid_out(struct vivid_dev *dev, bool *pstreaming)
     ^
drivers/media/platform/vivid/vivid-kthread-out.c:260:6: warning: no previous prototype for 'vivid_stop_generating_vid_out' [-Wmissing-prototypes]
 void vivid_stop_generating_vid_out(struct vivid_dev *dev, bool *pstreaming)
      ^
drivers/media/platform/vivid/vivid-kthread-cap.c:806:5: warning: no previous prototype for 'vivid_start_generating_vid_cap' [-Wmissing-prototypes]
 int vivid_start_generating_vid_cap(struct vivid_dev *dev, bool *pstreaming)
     ^
drivers/media/platform/vivid/vivid-kthread-cap.c:841:6: warning: no previous prototype for 'vivid_stop_generating_vid_cap' [-Wmissing-prototypes]
 void vivid_stop_generating_vid_cap(struct vivid_dev *dev, bool *pstreaming)
      ^

Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>