DisplayLink devices can be connected at runtime (through USB), allowing one to easily connect extra displays, just as if it was a docking station. With the first patch, mutter will look for non-pci devices. That fixes coldplug support. With the second one, mutter will look for upcoming devices at runtime, fixing hotplug support.
Note that the evdi driver doesn't remove the node when the device is disconnected, so we don't need to handle unplug here. Obviously the monitors are disconnected, but that's already handled.