tlv: Import osmo_shift_* and osmo_match_shift_* from openbsc

These routines have nothing to do with specifically the BSC, so import
them to the TLV parser we keep in libosmogsm.
diff --git a/tests/tlv/tlv_test.ok b/tests/tlv/tlv_test.ok
new file mode 100644
index 0000000..de159bf
--- /dev/null
+++ b/tests/tlv/tlv_test.ok
@@ -0,0 +1,2 @@
+Test shift functions
+Done.