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/include/osmocom/sgsn/gprs_mm_state_gb_fsm.h b/include/osmocom/sgsn/gprs_mm_state_gb_fsm.h
new file mode 100644
index 0000000..e69e1e1
--- /dev/null
+++ b/include/osmocom/sgsn/gprs_mm_state_gb_fsm.h
@@ -0,0 +1,26 @@
+#pragma once
+
+#include <osmocom/core/fsm.h>
+
+struct sgsn_mm_ctx;
+
+
+/* TS 23.060 6.1.1 Mobility Management States (A/Gb mode) */
+enum mm_state_gb_fsm_states {
+	ST_MM_IDLE,
+	ST_MM_READY,
+	ST_MM_STANDBY
+};
+
+enum mm_state_gb_fsm_events {
+	E_MM_GPRS_ATTACH,
+	/* E_GPRS_DETACH, TODO: not used */
+	E_MM_PDU_RECEPTION,
+	E_MM_IMPLICIT_DETACH, /* = E_MM_CANCEL_LOCATION */
+	E_MM_READY_TIMER_EXPIRY,
+	/* E_FORCE_TO_STANDBY, TODO: not used */
+	/* E_ABNSORMAL_RLC_CONDITION, TODO: not used */
+	E_MM_RA_UPDATE,
+};
+
+extern struct osmo_fsm mm_state_gb_fsm;