vduse: Signal vq trigger eventfd directly if possible

Now the vdpa callback will associate an trigger
eventfd in some cases. For performance reasons,
VDUSE can signal it directly during irq injection.

Signed-off-by: Xie Yongji <xieyongji@bytedance.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Message-Id: <20230323053043.35-10-xieyongji@bytedance.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>