sandbox: Enable time unit test command

Enable this command for sandbox.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/sandbox_defconfig b/configs/sandbox_defconfig
index 759f53a..70ae531 100644
--- a/configs/sandbox_defconfig
+++ b/configs/sandbox_defconfig
@@ -27,3 +27,4 @@
 CONFIG_CMD_SOUND=y
 CONFIG_SOUND_SANDBOX=y
 CONFIG_DM_RTC=y
+CONFIG_CMD_UT_TIME=y