Update DebugLib to provide support for "err" command in the EFI Shell to adjust the...

Update DebugLib to provide support for "err" command in the EFI Shell to adjust the filter mask for DEBUG() messages.  The "err" command provide the ability to adjust this filter mask at a global level through an EFI Variable and at the module level through a the Debug Mask Protocol.  In order to support the degree of flexibility, the DebugLib needs to use library to abstract the get/set operations to the filter mask.

1) Add default mappings for the DebugPrintErrorLevelLib to the DSC file for this package.

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@11377 6f19259b-4bc3-4df7-8a09-765794883524