ARM: ux500: Correctly reference IRQs supplied by the AB8500 from Device Tree

The AB8500 driver has now been provided with IRQ domain support. This
means we can request IRQs from any of it's uses via Device Tree. This
patch advertises the AB8500 as an Interrupt Controller and provides the
correct calls in the format the driver expects.

Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>