MdeModulePkg/Core/Dxe: Call new API InitializeCpuExceptionHandlersEx instead

MdeModulePkg/Core/Dxe: Call new API InitializeCpuExceptionHandlersEx instead

Original API InitializeCpuExceptionHandlers is used in DxeMain to initialize
exception handlers but it does not support setting up stack switch required
by Stack Guard feature. Using the new API instead to make sure Stack Guard
feature is applicable to most part of code.

Since this API is called before memory service initialization, there's no
way to call AllocateXxx API to reserve memory. Global variables are used
for this special case. GDT table is reserved at least 2KB which should be
big enough for all current use cases.

Cc: Star Zeng <star.zeng@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Suggested-by: Ayellet Wolman <ayellet.wolman@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Jian J Wang <jian.j.wang@intel.com>
Reviewed-by: Jeff Fan <vanjeff_919@hotmail.com>
Reviewed-by: Jiewen.yao@intel.com