audio/alsa-plugins: Fix SPEEX option, and symlinks.

Fixes these errors:

Error: /usr/local/lib/alsa-lib/libasound_module_pcm_speex.so is linked

to /usr/local/lib/libspeexdsp.so.1 from audio/speexdsp but it is not
declared as a dependency

Error: Orphaned: etc/alsa/conf.d/60-speex.conf
Error: Orphaned: share/alsa/alsa.conf.d/60-speex.conf

Also makes symlinks from etc/alsa/conf.d to share/alsa/alsa.conf.d/
relative to fix stage-qa warnings.