arm64: dts: Foundation model: increase GICC region to allow EOImode=1

The Foundation model GIC mapping is wrong, as the GICC region should
be 8kB instead of 4kB (the model implements the GICv2 architecture).
This defect prevents the driver from switching to EOImode==1.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>