irqchip: GICv3: rework redistributor structure

The basic GICv3 driver has almost no use for the redistributor
(other than the basic per-CPU interrupts), but the ITS needs
a lot more from them.

As such, rework the set of data structures. The behaviour of the
GICv3 driver is otherwise unaffected.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Link: https://lkml.kernel.org/r/1416839720-18400-4-git-send-email-marc.zyngier@arm.com
Signed-off-by: Jason Cooper <jason@lakedaemon.net>