UefiCpuPkg/CpuS3DataDxe: Move StartupVector allocation to EndOfDxe()

UefiCpuPkg/CpuS3DataDxe: Move StartupVector allocation to EndOfDxe()

Currently, we will allocate StartupVector buffer under 1MB at entry point
function. But some modules may allocate some hard code address under 1MB.
For example, LegacyBiosDxe driver tries to manage some legacy range under
640KB.

To avoid the conflicts, we move StartupVector buffer allocation to End Of
DXE event callback function.

v4:
  Update the Context parameter is used as a pointer to AcpiCpuDataEx, then
  we needn't to add the global variable.

Cc: Michael Kinney <michael.d.kinney@intel.com>
Cc: Feng Tian <feng.tian@intel.com>
Cc: Giri P Mudusuru <giri.p.mudusuru@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jeff Fan <jeff.fan@intel.com>
Reviewed-by: Giri P Mudusuru <giri.p.mudusuru@intel.com>
Reviewed-by: Michael Kinney <michael.d.kinney@intel.com>
Tested-by: Laszlo Ersek <lersek@redhat.com>
Tested-by: Michael Kinney <michael.d.kinney@intel.com>