[media] v4l2-dev: improve ioctl validity checks

The ioctl validity checks have been improved and now take vfl_type
and vfl_dir into account.
During the 2012 Media Workshop it was decided that these improved
v4l2 core checks should be added as they simplified drivers and
made drivers behave consistently.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>