MdePkg: Add new API DebugPrintLevelEnabled() in DebugLib

MdePkg: Add new API DebugPrintLevelEnabled() in DebugLib

This API is applied in _DEBUG_PRINT() macro for build time size optimization.
DebugLib library instance should implement this API to return the constant value.
DEBUG_PRINT() will base on __VA_ARGS__ for build time size optimization.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Liming Gao <liming.gao@intel.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@16787 6f19259b-4bc3-4df7-8a09-765794883524