Introduce FSM mm_state_gb_fsm

Implement TS 23.060 6.1.1 Mobility Management States (A/Gb mode) using
osmocom FSM and drop old implementation.
Most of the logic on each state is still kept in gprs_gmm.c, will be
inserted into the FSM later.

Change-Id: I04004423e993107374d5a3549b8a93ac169251dd
diff --git a/tests/sgsn/Makefile.am b/tests/sgsn/Makefile.am
index b035468..8a26d88 100644
--- a/tests/sgsn/Makefile.am
+++ b/tests/sgsn/Makefile.am
@@ -50,6 +50,7 @@
 	$(top_builddir)/src/gprs/gprs_sndcp.o \
 	$(top_builddir)/src/gprs/gprs_gmm_attach.o \
 	$(top_builddir)/src/gprs/gprs_gmm.o \
+	$(top_builddir)/src/gprs/gprs_mm_state_gb_fsm.o \
 	$(top_builddir)/src/gprs/gprs_sgsn.o \
 	$(top_builddir)/src/gprs/sgsn_vty.o \
 	$(top_builddir)/src/gprs/sgsn_libgtp.o \