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>
Acked-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>