gpio: Provide the tc3589x GPIO expander driver with an IRQ domain

In preparation for Device Tree enablement all IRQ controllers
should control their own IRQ domain. This patch provides just
that for the tc3589x GPIO expander.

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>