test: Add a simple time test

Sometimes the time functions are incorrect due to bad time support on a
board. Add a unit test which tries to detect this.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/test/Kconfig b/test/Kconfig
index 1fb1716..3270c84 100644
--- a/test/Kconfig
+++ b/test/Kconfig
@@ -1 +1,9 @@
+config CMD_UT_TIME
+	bool "Unit tests for time functions"
+	help
+	  Enables the 'ut_time' command which tests that the time functions
+	  work correctly. The test is fairly simple and will not catch all
+	  problems. But if you are having problems with udelay() and the like,
+	  this is a good place to start.
+
 source "test/dm/Kconfig"