dde_bsd: rename audio driver to audio_out_drv
dde_bsd: add driver files for Ensoniq ES1370

Apparently there are issue with OpenBSD's HDA driver in Qemu and it
would be nice indeed to have a driver which works in Qemu. Since it
fits the bill, let us pull ES1370 in.
dde_bsd: define NMIDI

NMIDI is defined in "midi.h" which is normally generated by config(8).
Since MIDI support is not necessary, we disable it.
dde_bsd: add extern C wrapping header
dde_bsd: add fn to trigger linkage of contrib code

By calling probe_audio() we get ourselves a nice looking dummy list.