MdeModulePkg: Add EDKII_PI_SMM_COMMUNICATION_REGION_TABLE definition.

MdeModulePkg: Add EDKII_PI_SMM_COMMUNICATION_REGION_TABLE definition.

This configuration table is used to describe platform pre-allocated memory
for SMM communication buffer. If DXE driver wants to communicate with SMM
agent, it can use this memory as SMM communication buffer instead of allocate
new memory region.

This is designed to meet Microsoft WSMT table definition on FIXED_COMM_BUFFERS
requirement.

Cc: Feng Tian <feng.tian@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jiewen Yao <jiewen.yao@intel.com>
Reviewed-by: Feng Tian <feng.tian@intel.com>