Axis devices support device registry (#22367)

* Add support for device registry

* Fix test

homeassistant/components/axis/binary_sensor.py

@@ -81,7 +81,20 @@ class AxisBinarySensor(BinarySensorDevice):
         """Return the class of the event."""
         return self.event.event_class
 
+    @property
+    def unique_id(self):
+        """Return a unique identifier for this device."""
+        return '{}-{}-{}'.format(
+            self.device.serial, self.event.topic, self.event.id)
+
     @property
     def should_poll(self):
         """No polling needed."""
         return False
+
+    @property
+    def device_info(self):
+        """Return a device description for device registry."""
+        return {
+            'identifiers': {(AXIS_DOMAIN, self.device.serial)}
+        }