tests: Introduce DT overlay tests

This adds a bunch of unit tests for the "fdt apply" command.

They've all been run successfully in the sandbox. However, as you still
require an out-of-tree dtc with overlay support, this is disabled by
default.

Acked-by: Simon Glass <sjg@chromium.org>
Acked-by: Pantelis Antoniou <pantelis.antoniou@konsulko.com>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
diff --git a/test/overlay/Makefile b/test/overlay/Makefile
new file mode 100644
index 0000000..907f085
--- /dev/null
+++ b/test/overlay/Makefile
@@ -0,0 +1,15 @@
+#
+# Copyright (c) 2016 NextThing Co
+# Copyright (c) 2016 Free Electrons
+#
+# SPDX-License-Identifier:	GPL-2.0+
+#
+
+# Test files
+obj-y += cmd_ut_overlay.o
+
+DTC_FLAGS += -@
+
+# DT overlays
+obj-y += test-fdt-base.dtb.o
+obj-y += test-fdt-overlay.dtb.o