bts/tbf: Move the lists into the BTS and do the look-up from the BTS

The list belongs to the BTS. This makes cleaning this up more easy
and establishes a hierachy of resources that start from the BTS. The
debug_diagram code is now broken.
diff --git a/src/encoding.cpp b/src/encoding.cpp
index 26ac71e..e28fff7 100644
--- a/src/encoding.cpp
+++ b/src/encoding.cpp
@@ -21,6 +21,7 @@
 
 #include <encoding.h>
 #include <gprs_rlcmac.h>
+#include <bts.h>
 #include <tbf.h>
 #include <gprs_debug.h>