virtio-rng: move qdev properties into virtio-rng.c

As only one place in virtio-rng.c uses DEFINE_VIRTIO_RNG_PROPERTIES,
there is no need to expose it. Inline it into virtio-rng.c to avoid
wrongly use.

Signed-off-by: Shannon Zhao <zhaoshenglong@huawei.com>
Signed-off-by: Shannon Zhao <shannon.zhao@linaro.org>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Acked-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
