Install systemd services with autotools

Change-Id: I103bf3468d53578045593eac31b61f7e0248495e
diff --git a/contrib/systemd/Makefile.am b/contrib/systemd/Makefile.am
new file mode 100644
index 0000000..b644f34
--- /dev/null
+++ b/contrib/systemd/Makefile.am
@@ -0,0 +1,9 @@
+if HAVE_SYSTEMD
+SYSTEMD_SERVICES = \
+  osmo-gbproxy.service \
+  osmo-gtphub.service \
+  osmo-sgsn.service
+
+EXTRA_DIST = $(SYSTEMD_SERVICES)
+systemdsystemunit_DATA = $(SYSTEMD_SERVICES)
+endif