libao: add PACKAGECONFIG for alsa and pulseaudio

* fixes following issues from test-dependencies report:
  Found errors:
  libao/libao-plugin-libalsa/latest doesn't exist
  libao/libao-plugin-libalsa-dbg/latest doesn't exist
  libao/libao-plugin-libpulse/latest doesn't exist
  libao/libao-plugin-libpulse-dbg/latest doesn't exist

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>