finish openbsc / libosmocore separation

* use pkg-config from openbsc to find header and library
* move sms and timer tests to libosmocore itself
* ensure "make distcheck" works on both packages
diff --git a/libosmocore/tests/Makefile.am b/libosmocore/tests/Makefile.am
new file mode 100644
index 0000000..56e8b6f
--- /dev/null
+++ b/libosmocore/tests/Makefile.am
@@ -0,0 +1 @@
+SUBDIRS = timer sms