dm: i2c: Add a sandbox I2C driver

This driver includes some test features such as only supporting certain
bus speeds. It passes its I2C traffic through to an emulator.

Acked-by: Heiko Schocher <hs@denx.de>
Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
diff --git a/drivers/i2c/Makefile b/drivers/i2c/Makefile
index 5a93473..6f3c86c 100644
--- a/drivers/i2c/Makefile
+++ b/drivers/i2c/Makefile
@@ -27,7 +27,7 @@
 obj-$(CONFIG_SYS_I2C_PPC4XX) += ppc4xx_i2c.o
 obj-$(CONFIG_SYS_I2C_RCAR) += rcar_i2c.o
 obj-$(CONFIG_SYS_I2C_S3C24X0) += s3c24x0_i2c.o
-obj-$(CONFIG_SYS_I2C_SANDBOX) += i2c-emul-uclass.o
+obj-$(CONFIG_SYS_I2C_SANDBOX) += sandbox_i2c.o i2c-emul-uclass.o
 obj-$(CONFIG_SYS_I2C_SH) += sh_i2c.o
 obj-$(CONFIG_SYS_I2C_SOFT) += soft_i2c.o
 obj-$(CONFIG_SYS_I2C_TEGRA) += tegra_i2c.o