UefiCpuPkg/CpuS3DataDxe: Keep old data if value already existed.

UefiCpuPkg/CpuS3DataDxe: Keep old data if value already existed.

AcpiCpuData add new fields, keep these fields if old data already existed.

Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Eric Dong <eric.dong@intel.com>
Reviewed-by: Ruiyu Ni <ruiyu.ni@intel.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Regression-tested-by: Laszlo Ersek <lersek@redhat.com>