product/rdn2: add a macro to generate sds ids

Simplify the definition of SDS structure ID enum values by using a new
macro 'SDS_STRUCT_ID'. This macro appends the SDS ID value and the major
version of the SDS structure ID.

Signed-off-by: Nishant Sharma <nishant.sharma@arm.com>
Change-Id: I124b9df5377e43c219083a5d3e68fc7742af3cc4