Platform/Sgi: Add initial support for RD-N2-Cfg1 platform

Arm's RD-N2-Cfg1 platform is a variant of the RD-N2 platform. Compared
to RD-N2 platform, RD-N2-Cfg1 has a reduced core count of eight Neoverse
N2 CPUs and a smaller interconnect mesh. As part of the initial platform
support for RD-N2-Cfg1 platform, add the corresponding ACPI tables,
platform and flash description files.

Signed-off-by: Pranav Madhu <pranav.madhu@arm.com>
Reviewed-by: Thomas Abraham <thomas.abraham@arm.com>
Reviewed-by: Sami Mujawar <sami.mujawar@arm.com>