[media] media: davinci: vpif_capture: initialize the video device in single place

this patch moves the initalization of video device to a
single place and uses macro to define the driver name and
use it appropriately on the required places.

Signed-off-by: Lad, Prabhakar <prabhakar.csengg@gmail.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>