test: dm: add tests for tag support

The new test covers all tag-related interfaces.

Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/test/dm/Makefile b/test/dm/Makefile
index 9a1a904..f0a7c97 100644
--- a/test/dm/Makefile
+++ b/test/dm/Makefile
@@ -102,6 +102,7 @@
 obj-$(CONFIG_RESET_SYSCON) += syscon-reset.o
 obj-$(CONFIG_SYSINFO) += sysinfo.o
 obj-$(CONFIG_SYSINFO_GPIO) += sysinfo-gpio.o
+obj-$(CONFIG_UT_DM) += tag.o
 obj-$(CONFIG_TEE) += tee.o
 obj-$(CONFIG_TIMER) += timer.o
 obj-$(CONFIG_DM_USB) += usb.o