introduce GSM primitive definitions

The idea here is to use the osmocom core primitive code ot abstract out
primitives for inter-layer comunication in GSM.
diff --git a/include/osmocom/gsm/Makefile.am b/include/osmocom/gsm/Makefile.am
index 547933e..aa7b1a9 100644
--- a/include/osmocom/gsm/Makefile.am
+++ b/include/osmocom/gsm/Makefile.am
@@ -1,6 +1,6 @@
 osmogsm_HEADERS = a5.h comp128.h gsm0808.h gsm48_ie.h mncc.h rxlev_stat.h \
 		  gsm0480.h gsm48.h gsm_utils.h rsl.h tlv.h abis_nm.h \
-		  sysinfo.h
+		  sysinfo.h prim.h
 
 SUBDIRS = protocol
 
diff --git a/include/osmocom/gsm/prim.h b/include/osmocom/gsm/prim.h
new file mode 100644
index 0000000..95cbb12
--- /dev/null
+++ b/include/osmocom/gsm/prim.h
@@ -0,0 +1,13 @@
+#ifndef OSMO_GSM_PRIM_H
+#define OSMO_GSM_PRIM_H
+
+#include <osmocom/core/prim.h>
+
+/* enumeration of GSM related SAPs */
+enum osmo_gsm_sap {
+	SAP_GSM_PH	= _SAP_GSM_BASE,
+	SAP_GSM_DL,
+	SAP_GSM_MDL,
+};
+
+#endif