virtio-serial-bus: move qdev properties into virtio-serial-bus.c
As only one place in virtio-serial-bus.c uses
DEFINE_VIRTIO_SERIAL_PROPERTIES, there is no need to expose it. Inline
it into virtio-serial-bus.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>