vDPA: add get_vq_irq() in vdpa_config_ops

This commit adds a new function get_vq_irq() in struct
vdpa_config_ops, which will return the irq number of a
virtqueue.
Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com>
Suggested-by: Jason Wang <jasowang@redhat.com>
Link: https://lore.kernel.org/r/20200731065533.4144-4-lingshan.zhu@intel.comSigned-off-by: Michael S. Tsirkin <mst@redhat.com>

include/linux/vdpa.h

@@ -89,6 +89,12 @@ struct vdpa_device {
  *				@vdev: vdpa device
  *				@idx: virtqueue index
  *				Returns the notifcation area
+ * @get_vq_irq:			Get the irq number of a virtqueue (optional,
+ *				but must implemented if require vq irq offloading)
+ *				@vdev: vdpa device
+ *				@idx: virtqueue index
+ *				Returns int: irq number of a virtqueue,
+ *				negative number if no irq assigned.
  * @get_vq_align:		Get the virtqueue align requirement
  *				for the device
  *				@vdev: vdpa device
@@ -180,6 +186,7 @@ struct vdpa_config_ops {
 	u64 (*get_vq_state)(struct vdpa_device *vdev, u16 idx);
 	struct vdpa_notification_area
 	(*get_vq_notification)(struct vdpa_device *vdev, u16 idx);
+	int (*get_vq_irq)(struct vdpa_device *vdv, u16 idx);
 
 	/* Device ops */
 	u32 (*get_vq_align)(struct vdpa_device *vdev);