UefiCpuPkg/AcpiCpuData: update comments on register table fields
    
    After commit e992cc3f4859 ("UefiCpuPkg PiSmmCpuDxeSmm: Reduce SMRAM
    consumption in CpuS3.c", 2021-01-11), it is valid for a CPU S3 Data DXE
    Driver to set "ACPI_CPU_DATA.PreSmmInitRegisterTable" and/or
    "ACPI_CPU_DATA.RegisterTable" to 0, in case none of the CPUs needs a
    register table of the corresponding kind, during S3 resume.
    
    Document this fact in the "UefiCpuPkg/Include/AcpiCpuData.h" header file.
    
    Cc: Eric Dong <eric.dong@intel.com>
    Cc: Philippe Mathieu-Daudé <philmd@redhat.com>
    Cc: Rahul Kumar <rahul1.kumar@intel.com>
    Cc: Ray Ni <ray.ni@intel.com>
    Cc: Star Zeng <star.zeng@intel.com>
    Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=3159
    Signed-off-by: Laszlo Ersek <lersek@redhat.com>
    Reviewed-by: Ray Ni <ray.ni@intel.com>
    Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>