Platform/Sgi: Define RD-N2-Cfg1 platform id values

Add the RD-N2-Cfg1 platform identification values including the part
number and configuration number. This information will be used in
populating the SMBIOS tables.

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>