UefiCpuPkg/PiSmmCpuDxeSmm: Fix S3 failure in SmmRestoreCpu

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=4368



This issue is caused by the commit:
ec07fd0e

GetFirstGuidHob() should not be used after exit boot service.

Cc: Eric Dong <eric.dong@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Cc: Zeng Star <star.zeng@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Jiaxin Wu <jiaxin.wu@intel.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>
Reviewed-by: Gerd Hoffmann <kraxel@redhat.com>
Tested-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Ray Ni <ray.ni@intel.com>