dm: spi: Add tests

These tests use SPI flash (and the sandbox emulation) to operate.

Signed-off-by: Simon Glass <sjg@chromium.org>
Acked-by: Jagannadha Sutradharudu Teki <jagannadh.teki@gmail.com>
diff --git a/test/dm/Makefile b/test/dm/Makefile
index 5c2415e..d1b9c9a 100644
--- a/test/dm/Makefile
+++ b/test/dm/Makefile
@@ -18,4 +18,5 @@
 obj-$(CONFIG_DM_TEST) += ut.o
 ifneq ($(CONFIG_SANDBOX),)
 obj-$(CONFIG_DM_GPIO) += gpio.o
+obj-$(CONFIG_DM_SPI) += spi.o
 endif