test: smem: add basic smem test

Add basic smem sandbox testing.

Signed-off-by: Ramon Fried <ramon.fried@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/test/dm/Makefile b/test/dm/Makefile
index 5511a85..d2ed96c 100644
--- a/test/dm/Makefile
+++ b/test/dm/Makefile
@@ -33,6 +33,7 @@
 obj-$(CONFIG_SYSRESET) += sysreset.o
 obj-$(CONFIG_DM_RTC) += rtc.o
 obj-$(CONFIG_DM_SPI_FLASH) += sf.o
+obj-$(CONFIG_SMEM) += smem.o
 obj-$(CONFIG_DM_SPI) += spi.o
 obj-y += syscon.o
 obj-$(CONFIG_DM_USB) += usb.o