MdeModulePkg/SmmMemoryAttribute.h: Add new protocol definitions

The new protocol gEdkiiSmmMemoryAttributeProtocolGuid is intended for
PiSmmCore to be able to change memory page attributes for the sake of
heap guard feature.

This protocol provides three interfaces to get/set/clear page attribute.

struct _EDKII_SMM_MEMORY_ATTRIBUTE_PROTOCOL {
  EDKII_SMM_GET_MEMORY_ATTRIBUTES       GetMemoryAttributes;
  EDKII_SMM_SET_MEMORY_ATTRIBUTES       SetMemoryAttributes;
  EDKII_SMM_CLEAR_MEMORY_ATTRIBUTES     ClearMemoryAttributes;
};

Cc: Star Zeng <star.zeng@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Suggested-by: Ayellet Wolman <ayellet.wolman@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Jian J Wang <jian.j.wang@intel.com>
Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>
Reviewed-by: Ruiyu Ni <ruiyu.ni@intel.com>
Regression-tested-by: Laszlo Ersek <lersek@redhat.com>