add new 'osmo-arfcn' program to compute frequency based on arfcn

The freq -> arfcn side still needs to be implemented.
diff --git a/configure.ac b/configure.ac
index b923a21..0ee8aa6 100644
--- a/configure.ac
+++ b/configure.ac
@@ -120,4 +120,5 @@
 	tests/msgfile/Makefile
 	tests/ussd/Makefile
 	tests/smscb/Makefile
+	utils/Makefile
 	Makefile)