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/Makefile b/test/Makefile
index 9c95805..08330e0 100644
--- a/test/Makefile
+++ b/test/Makefile
@@ -6,3 +6,4 @@
 
 obj-$(CONFIG_SANDBOX) += command_ut.o
 obj-$(CONFIG_SANDBOX) += compression.o
+obj-$(CONFIG_CMD_UT_TIME) += time_ut.o