dev-arm: Add VExpress_GEM5_Foundation platform

dev-arm: Add VExpress_GEM5_Foundation platform

A new VExpress_GEM5_Foundation platform has been added in order to match
the FVP Armv8-A Foundation Platform described in:

Armv8-A Foundation Platform - User Guide - Version 11.8

The VExpress_GEM5_V1/V2 are already loosely based on the Foundation
platform, however there are some differences in the PCI regions (V1/V2)
and the GICv3 regions (V2).
We hence introduce the VExpress_GEM5_Foundation to match closely the
FVP Foundation Platform

Change-Id: I1604c64ce566308d888c3a630019494b9fae7acf
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/27388
Tested-by: Gem5 Cloud Project GCB service account <345032938727@cloudbuild.gserviceaccount.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Ciro Santilli <ciro.santilli@arm.com>