vhost/vdpa: Remove the restriction that only supports virtio-net devices

vhost/vdpa: Remove the restriction that only supports virtio-net devices

Since the config checks are done by the vDPA drivers, we can remove the
virtio-net restriction and we should be able to support all kinds of
virtio devices.

<linux/virtio_net.h> is not needed anymore, but we need to include
<linux/slab.h> to avoid compilation failures.

Signed-off-by: Xie Yongji <xieyongji@bytedance.com>
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Link: https://lore.kernel.org/r/20210315163450.254396-11-sgarzare@redhat.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>