[media] davinci: move struct vpif_interface to chan_cfg

struct vpif_interface is channel specific, not subdev specific.
Move it to the channel config.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Acked-by: Sekhar Nori <nsekhar@ti.com>
Acked-by: Lad, Prabhakar <prabhakar.lad@ti.com>
Tested-by: Lad, Prabhakar <prabhakar.lad@ti.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>