Platform/ARM/SgiPkg: Add SRAT table for RdN1Edge dual-chip platform

The RD-N1-Edge dual chip platform has an additional 8GB of memory
connected to the second chip. Add the SRAT ACPI table to describe
the proximity domain, base address and size of this memory.

Signed-off-by: Aditya Angadi <aditya.angadi@arm.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@arm.com>