arm: mvebu: use global interrupts for GPIOs on Armada XP

The Armada XP GPIO controller has two ways of notifying interrupts:
using global interrupts or using per-CPU interrupts. In an attempt to
use the best available features, the 'marvell,armadaxp-gpio'
compatible string selects a variant of the gpio-mvebu driver that
makes use of the per-CPU interrupts.

Unfortunately, this doesn't work properly in a SMP context, because we
fall into cases where the GPIO interrupt is enabled on CPU X at the
GPIO controller level, but on CPU Y at the interrupt controller
level. It is not yet clear how to fix that easily.

So for 3.8, our approach is to switch to global interrupts for GPIOs,
so that we do not fall into this per-CPU interrupts problem.

This patch therefore fixes GPIO interrupts on Armada XP
platforms. Without this patch, GPIO interrupts simply do not work
reliably, because their proper operation depends on which CPU the code
requesting the interrupt is running.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>