Add clatd_test to presubmit.

Following the instructions at:
https://source.android.com/compatibility/tests/development/test-mapping

Test: cd external/android-clat; atest
Change-Id: Ifca302f53b38d47200d6a1651280391297f14edc
diff --git a/TEST_MAPPING b/TEST_MAPPING
new file mode 100644
index 0000000..c6d599d
--- /dev/null
+++ b/TEST_MAPPING
@@ -0,0 +1,7 @@
+{
+  "presubmit": [
+    {
+      "name": "clatd_test"
+    }
+  ]
+}