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

The freq -> arfcn side still needs to be implemented.
diff --git a/Makefile.am b/Makefile.am
index 03bfdec..d7a8fb7 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -2,7 +2,7 @@
 ACLOCAL_AMFLAGS = -I m4
 
 INCLUDES = $(all_includes) -I$(top_srcdir)/include
-SUBDIRS = include src tests
+SUBDIRS = include src tests utils
 
 pkgconfigdir = $(libdir)/pkgconfig
 pkgconfig_DATA = libosmocore.pc libosmocodec.pc libosmovty.pc libosmogsm.pc