Implement GMM State using osmocom FSM

State machine inspired in the one from TS 24.008 4.1.3.3.1. Some state
transitions are inroduced in the code but are still commented out since
we lack some functionalitites or improvements in the code to handle
different scenarios.

Most of the logic is still outside of the FSM, but at least now the
states are handled in a sane way triggered by events.

Change-Id: Idecb43c10d66224d4f9ba9320825040ce6cf9a07
diff --git a/tests/sgsn/Makefile.am b/tests/sgsn/Makefile.am
index 7ba70eb..9afe0f7 100644
--- a/tests/sgsn/Makefile.am
+++ b/tests/sgsn/Makefile.am
@@ -48,6 +48,7 @@
 	$(top_builddir)/src/sgsn/gprs_sndcp.o \
 	$(top_builddir)/src/sgsn/gprs_gmm_attach.o \
 	$(top_builddir)/src/sgsn/gprs_gmm.o \
+	$(top_builddir)/src/sgsn/gprs_gmm_fsm.o \
 	$(top_builddir)/src/sgsn/gprs_mm_state_gb_fsm.o \
 	$(top_builddir)/src/sgsn/gprs_mm_state_iu_fsm.o \
 	$(top_builddir)/src/sgsn/gprs_sgsn.o \