MdeModulePkg: Add definitions for EDKII DEBUG PPI

MdeModulePkg: Add definitions for EDKII DEBUG PPI

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=1549

Add a debug PPI for PEI phase. This PPI will provide basic
services of debug. PEI debug lib instance can use these
services to implement debug function to reduce the PEIMs
which consume the debug lib.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Zhichao Gao <zhichao.gao@intel.com>
Cc: Jian J Wang <jian.j.wang@intel.com>
Cc: Hao Wu <hao.a.wu@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Cc: Star Zeng <star.zeng@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Cc: Sean Brogan <sean.brogan@microsoft.com>
Cc: Michael Turner <Michael.Turner@microsoft.com>
Cc: Bret Barkelew <Bret.Barkelew@microsoft.com>
Reviewed-by: Hao Wu <hao.a.wu@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>