mfd: Provide the tc3589x with its own IRQ domain

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

Signed-off-by: Lee Jones <lee.jones@linaro.org>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>