UefiCpuPkg/MpInitLib: fix wrong address set as Stack Guard for APs

UefiCpuPkg/MpInitLib: fix wrong address set as Stack Guard for APs

The reason is that DXE part initialization will reuse the stack allocated
at PEI phase, if MP was initialized before. Some code added to check this
situation and use stack base address saved in HOB passed from PEI.

Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Jian J Wang <jian.j.wang@intel.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Eric Dong <eric.dong@intel.com>