dm: Move CONFIG_I2C_COMPAT to Kconfig

Make this option available in Kconfig and clean up the board that uses it.
Note there is also an entry in exynos5-common.h but this affects multiple
boards and should be dropped as part of the Samsung I2C migration to
driver model.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/i2c/Kconfig b/drivers/i2c/Kconfig
index 2cc776c..692810d 100644
--- a/drivers/i2c/Kconfig
+++ b/drivers/i2c/Kconfig
@@ -13,6 +13,15 @@
 	  enabled together (it is not possible to use driver model
 	  for one and not the other).
 
+config DM_I2C_COMPAT
+	bool "Enable I2C compatibility layer"
+	depends on DM
+	help
+	  Enable old-style I2C functions for compatibility with existing code.
+	  This option can be enabled as a temporary measure to avoid needing
+	  to convert all code for a board in a single commit. It should not
+	  be enabled for any board in an official release.
+
 config SYS_I2C_UNIPHIER
 	bool "UniPhier I2C driver"
 	depends on ARCH_UNIPHIER && DM_I2C