MdeModulePkg/PiSmmCore: Use unique structure signatures

MdeModulePkg/PiSmmCore: Use unique structure signatures

https://bugzilla.tianocore.org/show_bug.cgi?id=1948

Update the data structure signatures in the PiSmmCore
to be unique. Some of the signatures are the same as those
used by the DxeCore. For example, the memory pool head and
tail structures use the same signature in the PiSmmCore
and DxeCore.  This means the use of the wrong FreePool API
will not be noticed at the time FreePool is called and a
failure can occur much later.  By making the signatures
unique, misuse of an API is caught at that time the API is
called.

Cc: Jian J Wang <jian.j.wang@intel.com>
Cc: Hao A Wu <hao.a.wu@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Cc: Star Zeng <star.zeng@intel.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Signed-off-by: Michael D Kinney <michael.d.kinney@intel.com>
Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>
Reviewed-by: Jian J Wang <jian.j.wang@intel.com>
Reviewed-by: Eric Dong <eric.dong@intel.com>
Reviewed-by: Ray Ni <ray.ni@intel.com>