[media] media: davinci: vpif_capture: use v4l2_fh_open and vb2_fop_release

this patch adds support to use v4l2_fh_open() and vb2_fop_release,
which allows to drop driver specific struct vpif_fh, as this is handeled
by core. This patch also drops vpif_g/s_priority as this handeled
by core.

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>