Platform/ARM/SgiPkg: Enable MmCommunication module on the platform

The ArmMmCommunication module is used for communication between
non-secure and secure world using Arm's Management Mode
Specification. Enable this module on Sgi platforms. This would be used
subsequently by the RAS and SecureBoot features, support for which
is to be added on the platform.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Sughosh Ganu <sughosh.ganu@arm.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>