UefiCpuPkg/ExceptionLib: Conditionally clear shadow stack token busy bit

UefiCpuPkg/ExceptionLib: Conditionally clear shadow stack token busy bit

When enter SMM exception, there will be a stack switch only if the IST
field of the interrupt gate is set. When CET shadow stack feature is
enabled, if there is a stack switch between SMM exception and SMM, the
shadow stack token busy bit needs to be cleared when return from SMM
exception to SMM. In UEFI BIOS, only page fault exception does the stack
swith when SMM shack guard feature is enabled. The condition of clear
shadow stack token busy bit should be SMM stack guard enabled, CET shadows
stack feature enabled and page fault exception.
The shadow stack token should be initialized by UINT64.

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=3462

Signed-off-by: Sheng Wei <w.sheng@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Rahul Kumar <rahul1.kumar@intel.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Qihua Zhuang <qihua.zhuang@intel.com>
Cc: Daquan Dong <daquan.dong@intel.com>
Cc: Justin Tong <justin.tong@intel.com>
Cc: Tom Xu <tom.xu@intel.com>
Reviewed-by: Eric Dong <eric.dong@intel.com>