configure: add conditional library dependency for sofalizer and showfreqs

Signed-off-by: Paul B Mahol <onemda@gmail.com>

configure

@@ -6020,6 +6020,8 @@ enabled resample_filter && prepend avfilter_deps "avresample"
 enabled sab_filter          && prepend avfilter_deps "swscale"
 enabled scale_filter    && prepend avfilter_deps "swscale"
 enabled scale2ref_filter    && prepend avfilter_deps "swscale"
+enabled sofalizer_filter    && prepend avfilter_deps "avcodec"
+enabled showfreqs_filter    && prepend avfilter_deps "avcodec"
 enabled showspectrum_filter && prepend avfilter_deps "avcodec"
 enabled smartblur_filter    && prepend avfilter_deps "swscale"
 enabled subtitles_filter    && prepend avfilter_deps "avformat avcodec"