gpio: Enable the tc3298x GPIO expander driver for Device Tree

Here we provide a means to probe and extract vital information
from Device Tree when booting with it enabled. Without this
patch sub-devices wouldn't be able to reference the tc3589x-gpio
expander from Device Tree.

CC: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>