dm: i2c: Add tests for I2C

Add some basic tests to check that the system works as expected.

Signed-off-by: Simon Glass <sjg@chromium.org>
Acked-by: Heiko Schocher <hs@denx.de>
diff --git a/test/dm/Makefile b/test/dm/Makefile
index 75d3d41..612aa95 100644
--- a/test/dm/Makefile
+++ b/test/dm/Makefile
@@ -20,4 +20,5 @@
 obj-$(CONFIG_DM_GPIO) += gpio.o
 obj-$(CONFIG_DM_SPI) += spi.o
 obj-$(CONFIG_DM_SPI_FLASH) += sf.o
+obj-$(CONFIG_DM_I2C) += i2c.o
 endif