This driver depends on many things defined in ArmPkg (as it should) and shares not common code other architectures. Moving it to ArmPkg is part of removing dependencies in StandaloneMmPkg on ArmPkg. The Arm-specific implementation of StandaloneMmPkg/Library/StandaloneMmCoreEntryPoint library can move to ArmPkg or ArmPlatformPkg. The interface is already well-defined at lower layers. The implementation can live elsewhere. There is no common code with other architectures. Example/Proposed changes can be seen here for reference: https://github.com/microsoft/mu_silicon_arm_tiano/tree/release/202108/ArmPkg and https://github.com/microsoft/mu_basecore/tree/release/202108/StandaloneMmPkg
Include ARM maintainer ardb@kernel.org for the discussion.
