For quite some time now the device driver module doesn't work well
without the discovery module, so for the BlueZ 5 support we'll prevent
the device driver module to be loaded if the discovery module is not
loaded.
pa_bluetooth_discovery is the struct that holds information about known
Bluetooth audio devices and other information about the Bluetooth stack.
This commit also creates bluez5-util.[ch], which will hold a lot of
utility functions to help with the BlueZ 5 support.
