LCLS, TS 29.205: add GCR routines

Add functions to encode and decode Global Call Reference as per
3GPP TS 29.205 Table B 2.1.9.1 add corresponding tests.

Change-Id: Iee95aa4e5c056645b6cb5667e4a067097d52dfbf
Related: OS#2487
diff --git a/tests/gsm29205/gsm29205_test.ok b/tests/gsm29205/gsm29205_test.ok
new file mode 100644
index 0000000..bddd88a
--- /dev/null
+++ b/tests/gsm29205/gsm29205_test.ok
@@ -0,0 +1,5 @@
+Testing 3GPP TS 29.205 routines...
+Testing Global Call Reference encoder...
+	13 bytes added: OK
+	decoded 13 bytes: OK
+Done.