libsndfile is only needed by the sbctester utility and the library can
be built without this dependency.
Add a config option to cover not just sbctester but the command-line
utilities as well. While the utilities may be useful for debugging,
normal usage will only need libsbc and these applications can be
omitted.
Signed-off-by: John Keeping <john@metanate.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>