New str_nfc_target() function in API.

This allow to convert a nfc_target struct into allocated string.

examples/pn53x-sam.c

@@ -159,7 +159,7 @@ main(int argc, const char *argv[])
         goto error;
       } else if (res == 1) {
         printf("The following ISO14443A tag (SAM) was found:\n");
-        print_nfc_iso14443a_info(nt.nti.nai, true);
+        print_nfc_target(nt, true);
       } else {
         ERR("%s", "More than one ISO14442 tag found as SAM.");
         goto error;