As the ITS is always a subsystem if GICv3, its probing/init is
driven by the main GICv3 code.

Plug that code in (guarded by a config option).
Signed-off-by: NMarc Zyngier <marc.zyngier@arm.com>
Link: https://lkml.kernel.org/r/1416839720-18400-12-git-send-email-marc.zyngier@arm.comSigned-off-by: NJason Cooper <jason@lakedaemon.net>