audio: re-enable bits that depend on pbutils, disabled b/c of circular dependency

Submitted by Marvin Schmidt

Link to original bug (#657675)

Description

Trying to build current 0.11 branch (811a8961 playsink: fix ts_offset refcounting) fails with the following error:

[snip]
CC libgstpbutils_0.11_la-gstpluginsbaseversion.lo
CC libgstpbutils_0.11_la-pbutils.lo
CC libgstpbutils_0.11_la-codec-utils.lo
CC libgstpbutils_0.11_la-descriptions.lo
In file included from ../../../gst-libs/gst/audio/audio.h:27:0,
from descriptions.c:45:
../../../gst-libs/gst/audio/multichannel.h:21:39: fatal error: gst/audio/audio-enumtypes.h: No such file or directory
compilation terminated.
make[1]: *** [libgstpbutils_0.11_la-descriptions.lo] Error 1

audio-enumtypes.h wasn't yet created at that point, because the audio library is build after pbutils as it links against it

Due to
http://cgit.freedesktop.org/gstreamer/gst-plugins-base/commit/?h=0.11&id=c81c62d03a183eb524a88485a5a0f48d7f687588
pbutils depends on the audio and hence creating a circular dependency between the two.