plat/arm/sgi: refactor the inclusion of memory mapping

Upcoming RD platforms have a different memory map from those of the
existing platforms. So make the build of the existing mmap entries to be
usable only for existing platforms and let upcoming platforms define
a different set of mmap entries.

Change-Id: Id1ef0293efe8749c78a99237e78d32573c7233aa
Signed-off-by: Aditya Angadi <aditya.angadi@arm.com>
6 files changed