MdeModulePkg: Add definitions for Storage Security Command PPI

MdeModulePkg: Add definitions for Storage Security Command PPI

REF:https://bugzilla.tianocore.org/show_bug.cgi?id=1409

This commit will add the definitions for Storage Security Command (SSC)
PPI. This PPI will be be used to abstract mass storage devices to allow
code running in the PEI phase to send security protocol commands to mass
storage devices without specific knowledge of the type of device or
controller that manages the device.

More specifically, the PPI will provide services to:

* Get the number of mass storage devices managed by a instance of the SSC
  PPI (by service 'GetNumberofDevices');
* Get the identification information (DevicePath) of a managing mass
  storage devices (by service 'GetDevicePath');
* Send security protocol commands to mass storage devices (by services
  'ReceiveData' and 'SendData').

Cc: Jian J Wang <jian.j.wang@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Hao Wu <hao.a.wu@intel.com>
Reviewed-by: Ray Ni <ray.ni@intel.com>
Reviewed-by: Eric Dong <eric.dong@intel.com>