drivers: cci: add missing CCI port availability firmware check

The CCI ports programming interface is available to the kernel
only when booted in secure mode (or when firmware enables
non-secure access to override CCI ports control). In both cases,
firmware reports the CCI ports availability through the device
tree CCI ports nodes, which must be parsed and their status checked
by the kernel probing path.

This check is currently missing and may cause the kernel to
erroneously believe it is free to take control of CCI ports
where in practice CCI ports control is forbidden.

Add the missing CCI port availability check to the CCI driver
in order to guarantee sane CCI usage.

Cc: Liviu Dudau <liviu.dudau@arm.com>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Acked-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>