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 DebugMask.h that defines the GUID and Protocol used by the "err" EFI Shell command to get/set the global mask and get/set the module scoped masks
2) Add DxeDebugPrintErrorLevelLib that provide an implementation of the DebugPrintErrorLevbel library classes that uses the GUID and Protocol defined in DebugMask.h to "err" EFI Shell compatibility.
3) Add default mapping for the DebugPrintErrirLevelLib to the DSC file for this package.

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@11366 6f19259b-4bc3-4df7-8a09-765794883524