Add a GUIDed HOB to init Debug Print error level earlier in DXE. Add NULL PEIM library to init HOB.

Debug Print Error level can be controled by an EFI variable. Update the DXE version of the library to use a HOB if the variable services are not yet availilbe. This allows the variable to be used early in the DXE phase. 

approved-by: andrewfish
reviewed-by: lgao4



git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@12516 6f19259b-4bc3-4df7-8a09-765794883524

MdeModulePkg/Include/Guid/DebugMask.h

@@ -62,6 +62,7 @@ extern EFI_GUID gEfiDebugMaskProtocolGuid;
 
 ///
 /// GUID used to store the global debug mask in an the "EFIDebug" EFI Variabe
+/// Also used as a GUIDed HOB that contains a UINT32 debug mask default value
 ///
 #define EFI_GENERIC_VARIABLE_GUID \
   { 0x59d1c24f, 0x50f1, 0x401a, {0xb1, 0x01, 0xf3, 0x3e, 0x0d, 0xae, 0xd4, 0x43} }