Add CAS FOM state name in m0trace (Seagate#1680)

cas_fom_tick ENTRY record in m0trace includes numerical state ID.
This commit adds state name as text to that m0trace record.

Signed-off-by: Ivan Tishchenko <ivan.tishchenko@seagate.com>

cas/service.c

@@ -1184,7 +1184,9 @@ static int cas_fom_tick(struct m0_fom *fom0)
 	bool                do_ctidx;
 	int                 next_phase;
 
-	M0_ENTRY("fom %p phase %d op_flag=0x%x", fom, phase, op->cg_flags);
+	M0_ENTRY("fom %p phase %d (%s) op_flag=0x%x", fom, phase,
+		 m0_fom_phase_name(fom0, phase), op->cg_flags);
+
 	M0_PRE(ctidx != NULL);
 	M0_PRE(cas_fom_invariant(fom));
 	M0_PRE(ergo(is_dtm0_used, m0_dtm0_tx_desc__invariant(&op->cg_txd)));