Stop binding audio devices exposed by sndiod to physical devices

Stop binding audio devices exposed by sndiod to physical devices

This a shift towards a new model: clients connect to logical devices
(created with -s option) then the server routes data to/from the
underlying physical device (registered with -f option). The binding
may be changed at run-time with the server.device control exposed by
sndioctl(1).

As audio devices exposed by sndiod(8) are not bound to fixed physical
devices anymore, the physical audio device number component of
sndio(7) descriptors was removed.

fixes, help from and ok denis, edd