StandaloneMmPkg/Core: Implementation of Standalone MM Core Module.

StandaloneMmPkg/Core: Implementation of Standalone MM Core Module.

Management Mode (MM) is a generic term used to describe a secure
execution environment provided by the CPU and related silicon that is
entered when the CPU detects a MMI. For x86 systems, this can be
implemented with System Management Mode (SMM). For ARM systems, this can
be implemented with TrustZone (TZ).
A MMI can be a CPU instruction or interrupt. Upon detection of a MMI, a
CPU will jump to the MM Entry Point and save some portion of its state
(the "save state") such that execution can be resumed.
The MMI can be generated synchronously by software or asynchronously by
a hardware event. Each MMI source can be detected, cleared and disabled.
Some systems provide for special memory (Management Mode RAM or MMRAM)
which is set aside for software running in MM. Usually the MMRAM is
hidden during normal CPU execution, but this is not required. Usually,
after MMRAM is hidden it cannot be exposed until the next system reset.

The MM Core Interface Specification describes three pieces of the PI
Management Mode architecture:
1. MM Dispatch
   During DXE, the DXE Foundation works with the MM Foundation to
   schedule MM drivers for execution in the discovered firmware volumes.
2. MM Initialization
   MM related code opens MMRAM, creates the MMRAM memory map, and
   launches the MM Foundation, which provides the necessary services to
   launch MM-related drivers. Then, sometime before boot, MMRAM is
   closed and locked. This piece may be completed during the
   SEC, PEI or DXE phases.
3. MMI Management
   When an MMI generated, the MM environment is created and then the MMI

   sources are detected and MMI handlers called.

This patch implements the MM Core.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Sughosh Ganu <sughosh.ganu@arm.com>
Signed-off-by: Supreeth Venkatesh <supreeth.venkatesh@arm.com>
Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>