[media] media: blackfin: bfin_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 bcap_fh, as this is handled
by core.

Signed-off-by: Lad, Prabhakar <prabhakar.csengg@gmail.com>
Tested-by: Scott Jiang <scott.jiang.linux@gmail.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>