MdePkg-SmmMemLib: Enhance SmmIsBufferOutsideSmmValid() check for fixed comm buffer.

MdePkg-SmmMemLib: Enhance SmmIsBufferOutsideSmmValid() check for fixed comm buffer.

This patch adds more check in SmmIsBufferOutsideSmmValid(), to make sure that
SMM communication buffer is only EfiReservedMemoryType/EfiRuntimeServicesCode/
EfiRuntimeServicesData/EfiACPIMemoryNVS. So that the communication buffer will
not touch any OS memory.

The assumption is that a platform reports valid SMM communication buffer at
EndOfDxe, because EndOfDxe is last hook point that SMM code can call-out to
get memory map information.
A platform MUST finish SMM communication buffer allocation before EndOfDxe.
If a DXE or OS driver need do communication after EndOfDxe, it can either
allocate SMM communication buffer before EndOfDxe and save it, or consume
EDKII_PI_SMM_COMMUNICATION_REGION_TABLE table to get general fixed comm buffer.

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

Cc: Liming Gao <liming.gao@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: Liming Gao <liming.gao@intel.com>
Regression-tested-by: Laszlo Ersek <lersek@redhat.com>