Add value strings for Probable Cause Type

Add string representation of Probable Cause Type from 3GPP TS 12.21 ยง
9.4.43.

Change-Id: I9fe14ed3b5398f59dd06a509e4d419e074cc20a7
Related: OS#1615
diff --git a/src/gsm/libosmogsm.map b/src/gsm/libosmogsm.map
index 0c37d1c..3d1413d 100644
--- a/src/gsm/libosmogsm.map
+++ b/src/gsm/libosmogsm.map
@@ -27,6 +27,7 @@
 abis_nm_osmo_magic;
 abis_nm_ipa_magic;
 abis_nm_event_cause_names;
+abis_nm_pcause_type_names;
 
 osmo_sitype_strs;
 osmo_c4;