Check if the vb2 queue uses requests, and if so refuse to
add buffers that are not part of a request. Also check for
the reverse: a vb2 queue did not use requests, and an attempt
was made to queue a buffer to a request.

We might relax this in the future, but for now just return
-EPERM in that case.
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Reviewed-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>