StandaloneMmPkg: Add CPU driver suitable for ARM Platforms.

StandaloneMmPkg: Add CPU driver suitable for ARM Platforms.

This patch adds a simple CPU driver that exports the
EFI_MM_CONFIGURATION_PROTOCOL to allow registration of the Standalone
MM Foundation entry point. It preserves the existing notification
mechanism for the configuration protocol.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Sughosh Ganu <sughosh.ganu@arm.com>
Signed-off-by: Achin Gupta <achin.gupta@arm.com>
Signed-off-by: Supreeth Venkatesh <supreeth.venkatesh@arm.com>
Reviewed-by: Achin Gupta <achin.gupta@arm.com>