audit: new package

[Thomas:
 - remove S01audit, which isn't completely compliant with the
   Buildroot style.
 - make the package available only on architectures for which the
   system call tables are available, and add some comments about this
   in the .mk file.]

Signed-off-by: Clayton Shotwell <clayton.shotwell@rockwellcollins.com>
Signed-off-by: Matthew Weber <matthew.weber@rockwellcollins.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>