[media] media: davinci: vpif: display: separate out subdev from output

vpif_display relied on a 1-1 mapping of output and subdev. This is not
necessarily the case. Separate the two. So there is a list of subdevs
and a list of outputs. Each output refers to a subdev and has routing
information. An output does not have to have a subdev.
The initial output for each channel is set to the fist output.
Currently missing is support for associating multiple subdevs with
an output.

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