vexpress: disable cci ace slave ports when booting in non-sec/hyp mode

Commit f225d39d ("vexpress: Check TC2 firmware support before defaulting
to nonsec booting") added support to check if the firmware on TC2  is
configured appropriately before booting in nonsec/hyp mode.

However when booting in non-secure/hyp mode, CCI control must be done in
secure firmware and can't  be done in non-secure/hyp mode. In order to
ensure that, this patch disables the cci slave port inteface so that it
is not accessed at all.

Cc: Jon Medhurst <tixy@linaro.org>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
Acked-by: Jon Medhurst <tixy@linaro.org>
Tested-by: Jon Medhurst <tixy@linaro.org>