Platform/Sgi: Add CPU container for RD-N2 platform

The RD-N2 platform is a sixteen core platform with each core contained
in a minimal cluster logic. Update the processor device entries
accordingly in the DSDT ACPI table by moving each of the processor
device entries into a separate processor container devices.

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>