audio/musicpd: Add WAVPACK to OPTIONS_DEFAULT

Rationale:
If wavpack files containing DSD content are played via ffmpeg, they are
first converted to PCM in libavcodec (i.e. resampled and filtered), then
again to the native resolution of the oss output.
Using libwavpack directly allows mpd to leverages its native support for
DSD content, avoiding multiple resampling and / or filtering steps.

MFH: 2022Q4