Platform/Sgi: Add initial support for RD-Fremont platform

The RD-Fremont fixed virtual platform simulates 16 CPUs and 8GB of RAM.
Add initial support for this platform by adding the required platform
build configuration files. This platform has considerable differences in
its memory map compared to its predecessors. So add a corresponding
memory map file as well to define the PCDs for its generation of
platforms.

Signed-off-by: Prabin CA <prabin.ca@arm.com>