[media] vivid: enable vb2_expbuf support

Now that vb2 supports DMABUF export for dma-sg and vmalloc memory
modes, we can enable the vb2_expbuf support in vivid.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Reviewed-by: Pawel Osciak <pawel@osciak.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>