Audio devices are created in the audio subsystem and it is not possible
to send a device to bt service upon creation.
Introduce hookable audio device factory to allow sharing bluetooth
audio device. Move audio devices from bsp to audio allowing removal of
unwanted bsp -> audio dependency.
Remove Bluetooth proxy device which turned out to be a dead end.
Signed-off-by: Marcin Smoczyński <smoczynski.marcin@gmail.com>
