MdeModulePkg: Add definitions for NVM Express Passthru PPI

MdeModulePkg: Add definitions for NVM Express Passthru PPI

https://bugzilla.tianocore.org/show_bug.cgi?id=1879
This commit will add the definitions of Nvm Express PassThru PPI.
This PPI will provide services that allow NVM commands to be sent
to NVM Express devices during PEI phase.

More specifically, the PPI will provide services to:

* Sends an NVM Express Command Packet to an NVM Express controller
  or namespace (by service 'PassThru');
* Get the list of the attached namespaces on a controller
  (by services 'GetNextNameSpace');
* Get the identification information (DevicePath) of the underlying
  NVM Express host controller (by service 'GetDevicePath').

Signed-off-by: Maggie Chu <maggie.chu@intel.com>
Reviewed-by: Hao A Wu <hao.a.wu@intel.com>
Cc: Jian J Wang <jian.j.wang@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Cc: Star Zeng <star.zeng@intel.com>