tbf: Move existing tbf_state implementation to osmo_fsm

This is only an initial implementation, where all state changes are
still done outside the FSM itself.
The idea is to do the move in several commits so that they can be
digested better in logical steps and avoid major break up.

Related: OS#2709
Change-Id: I6bb4baea2dee191ba5bbcbec2ea9dcf681aa1237
diff --git a/doc/tbf.txt b/doc/tbf.txt
index f5b39c5..6abcb0b 100644
--- a/doc/tbf.txt
+++ b/doc/tbf.txt
@@ -14,16 +14,16 @@
     Queue of next frames to be transmitted.
 
 States:
-  GPRS_RLCMAC_ASSIGN
+  TBF_ST_ASSIGN
     After a downlink TBF is created, it resides in this state until the
     block flow can start. This is required to give the mobile time to listen
     to connect to downlink PDCH.
 
-   GPRS_RLCMAC_FLOW,
+   TBF_ST_FLOW,
     During packet flow, this state indicates downlink and uplink TBF block
     flow.
 
-   GPRS_RLCMAC_FINISHED,
+   TBF_ST_FINISHED,
     Uplink TBF:
     After final block is received AND all other blocks are completely
     received, the state is entered. The PACKET CONTROL ACK is still not
@@ -33,11 +33,11 @@
     downlink blocks are acknowledged yet. (Counter N3015 is counted on each
     poll request.)
 
-   GPRS_RLCMAC_WAIT_RELEASE,
+   TBF_ST_WAIT_RELEASE,
     The all blocks on downlink TBF have been acked by mobile. The penalty
     timer T3192 is running on mobile.
 
-   GPRS_RLCMAC_RELEASING,
+   TBF_ST_RELEASING,
     Wait for TFI/USF to be re-used. This state is entered when a counter
     reaches it's maximum and T3169 is running.