arm64: dts: vexpress: Support GICC_DIR operations

The GICv2 CPU interface registers span across 8K, not 4K as indicated in
the DT.  Only the GICC_DIR register is located after the initial 4K
boundary, leaving a functional system but without support for separately
EOI'ing and deactivating interrupts.

After this change the system supports split priority drop and interrupt
deactivation. This patch is based on similar one from Christoffer Dall:
commit 368400e2 ("ARM: dts: vexpress: Support GICC_DIR operations")

Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>