sox: add PACKAGECONFIG for flac, armwb, amrnb

* hopefully fixes:
  sox-14.4.0: sox rdepends on libflac, but it isn't a build dependency? [build-deps]
  sox-14.4.0: sox rdepends on opencore-amr, but it isn't a build dependency? [build-deps]

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