irqchip/gic-v3-its: Change initialization ordering for LPIs

We currently initialize the LPIs (and the ITS) fairly early, even
before the SMP support and the CPU interface. This is a bit odd
(as LPIs are not exactly crutial for the early boot process),
and is going to cause issues when reorganizing the probing code.

Let's move this initialization later.

Reviewed-by: Julien Thierry <julien.thierry@arm.com>
Tested-by: Jeremy Linton <jeremy.linton@arm.com>
Tested-by: Bhupesh Sharma <bhsharma@redhat.com>
Tested-by: Lei Zhang <zhang.lei@jp.fujitsu.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>