Separate the logic of creating desc_state, desc_extra, and subsequent
patches will call it independently.
Signed-off-by: NXuan Zhuo <xuanzhuo@linux.alibaba.com>
Acked-by: NJason Wang <jasowang@redhat.com>
Message-Id: <20220801063902.129329-12-xuanzhuo@linux.alibaba.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>