gsm_bts: add version and variant details

* add version string to gsm_bts
* add PCU version string to gsm_bts
* rename GSM_BTS_TYPE_OSMO_SYSMO -> GSM_BTS_OSMOBTS to avoid confusion
  between BTS model and variant
* add variant enum to gsm_bts_model using enum with variants for each
  hw vendor of OsmoBTS
* show connected PCU version (if available) in vty via 'show bts'

This will come in handy when logging details regarding particular BTS
reported via OML, see:

Related: OS#1614

Change-Id: I6710d53115f34634a7b70969cc05fd5c72ff8ab2
diff --git a/openbsc/include/openbsc/gsm_data.h b/openbsc/include/openbsc/gsm_data.h
index 08e07d8..1d90eee 100644
--- a/openbsc/include/openbsc/gsm_data.h
+++ b/openbsc/include/openbsc/gsm_data.h
@@ -469,7 +469,7 @@
 {
 	switch (bts->type) {
 	case GSM_BTS_TYPE_NANOBTS:
-	case GSM_BTS_TYPE_OSMO_SYSMO:
+	case GSM_BTS_TYPE_OSMOBTS:
 		return 1;
 	default:
 		break;
@@ -480,7 +480,7 @@
 static inline int is_sysmobts_v2(struct gsm_bts *bts)
 {
 	switch (bts->type) {
-	case GSM_BTS_TYPE_OSMO_SYSMO:
+	case GSM_BTS_TYPE_OSMOBTS:
 		return 1;
 	default:
 		break;