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/cmd_ut.c b/test/cmd_ut.c
index f6e1f41..1433342 100644
--- a/test/cmd_ut.c
+++ b/test/cmd_ut.c
@@ -19,6 +19,9 @@
 #if defined(CONFIG_UT_ENV)
 	U_BOOT_CMD_MKENT(env, CONFIG_SYS_MAXARGS, 1, do_ut_env, "", ""),
 #endif
+#ifdef CONFIG_UT_OVERLAY
+	U_BOOT_CMD_MKENT(overlay, CONFIG_SYS_MAXARGS, 1, do_ut_overlay, "", ""),
+#endif
 #ifdef CONFIG_UT_TIME
 	U_BOOT_CMD_MKENT(time, CONFIG_SYS_MAXARGS, 1, do_ut_time, "", ""),
 #endif
@@ -68,6 +71,9 @@
 #ifdef CONFIG_UT_ENV
 	"ut env [test-name]\n"
 #endif
+#ifdef CONFIG_UT_OVERLAY
+	"ut overlay [test-name]\n"
+#endif
 #ifdef CONFIG_UT_TIME
 	"ut time - Very basic test of time functions\n"
 #endif