AppPkg/WebServer: Fix build failure.
    
    Fix build failure caused by UefiCpuPkg/MtrrLib removes deprecated macros.
    related bugz: https://bugzilla.tianocore.org/show_bug.cgi?id=691
    
    Cc: Daryl McDaniel <edk2-lists@mc2research.org>
    Cc: Jaben Carsey <jaben.carsey@intel.com>
    Cc: Ruiyu Ni <ruiyu.ni@intel.com>
    Contributed-under: TianoCore Contribution Agreement 1.1
    Signed-off-by: Eric Dong <eric.dong@intel.com>
    Reviewed-by: Daryl McDaniel <edk2-lists@mc2research.org>
    Reviewed-by: Jaben Carsey <jaben.carsey@intel.com>