libcamera: media_device: Add disconnected signal

The signal is emitted when the hardware device corresponding to the
media device is unplugged. This will trigger the full unplug handling
chain.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>

src/libcamera/media_device.cpp

@@ -427,6 +427,16 @@ int MediaDevice::disableLinks()
 	return 0;
 }
 
+/**
+ * \var MediaDevice::disconnected
+ * \brief Signal emitted when the media device is disconnected from the system
+ *
+ * This signal is emitted when the device enumerator detects that the media
+ * device has been removed from the system. For hot-pluggable devices this is
+ * usually caused by physical device disconnection, but can also result from
+ * driver unloading for most devices. The media device is passed as a parameter.
+ */
+
 /**
  * \var MediaDevice::objects_
  * \brief Global map of media objects (entities, pads, links) keyed by their