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In preparation for adding the board support for RD-N2 platform, add
macros to define the platform id and the corresponding SCMI platform
info for the RD-N2 platform.

Change-Id: Ie764ae618732b39e316f7ed080421f5d79adab21
Signed-off-by: Aditya Angadi <aditya.angadi@arm.com>