src/basic: rename audit.[ch] → audit-util.[ch] and capability.[ch] → capability-util.[ch]

The files are named too generically, so that they might conflict with
the upstream project headers. Hence, let's add a "-util" suffix, to
clarify that this are just our utility headers and not any official
upstream headers.

src/tmpfiles/tmpfiles.c

@@ -40,7 +40,7 @@
 
 #include "acl-util.h"
 #include "btrfs-util.h"
-#include "capability.h"
+#include "capability-util.h"
 #include "chattr-util.h"
 #include "conf-files.h"
 #include "copy.h"