[media] davinci: convert vpif_capture to core-assisted locking

Now uses .unlocked_ioctl instead of .ioctl.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Acked-by: Manjunath Hadli <manjunath.hadli@ti.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>