arm64: dts: add .dts for GICv3 Foundation model

The ARMv8 Foundation model sports a command line parameter to use
a GICv3 emulation instead of the default GICv2 interrupt controller.
Add a new .dts file which reuses most of the definitions of the
existing model while just adding the required properties for the
GICv3 node.

This allows the public Foundation model to run with a GICv3.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>