mfd: tc3589x: Enforce device-tree only mode

All systems using the TC3589x multifunction expander uses
devicetree, so don't clutter the place with a lot of
and assume it is there.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
diff --git a/drivers/mfd/Kconfig b/drivers/mfd/Kconfig
index 5e68fde..ba097f7 100644
--- a/drivers/mfd/Kconfig
+++ b/drivers/mfd/Kconfig
@@ -1260,6 +1260,7 @@
 config MFD_TC3589X
 	bool "Toshiba TC35892 and variants"
 	depends on I2C=y
+	depends on OF
 	select MFD_CORE
 	help
 	  Support for the Toshiba TC35892 and variants I/O Expander.