sys/osxaudio/: Rewrite caps setting and ring buffer initialisation.

sys/osxaudio/: Rewrite caps setting and ring buffer initialisation.

Original commit message from CVS:
* sys/osxaudio/Makefile.am:
* sys/osxaudio/gstosxaudio.c:
* sys/osxaudio/gstosxaudiosink.c:
* sys/osxaudio/gstosxaudiosink.h:
* sys/osxaudio/gstosxaudiosrc.c:
* sys/osxaudio/gstosxaudiosrc.h:
* sys/osxaudio/gstosxringbuffer.c:
* sys/osxaudio/gstosxringbuffer.h:
Rewrite caps setting and ring buffer initialisation.
Previously we never told CoreAudio what format we were going to send it,
so it only worked due to luck, and not at all on some hardware.
Now we explicitly advertise what formats the hardware supports, and then
configure the selected one correctly.