AppPkg/WebServer: Fix build failure.

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>