[media] soc_camera: fix expbuf support

- For vb1 drivers just return -ENOTTY.
- For vb2 drivers allow vb2_expbuf without there being a stream owner:
  the vb2_expbuf function will return the correct error message in that case.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Acked-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>