UefiCpuPkg/MpInitLib: needn't to allocate AP reset vector

UefiCpuPkg/MpInitLib: needn't to allocate AP reset vector

Because we will always borrow the AP reset vector space for AP waking up. We
needn't allocate such range to prevent other module to use it. It could simply
the code.

https://bugzilla.tianocore.org/show_bug.cgi?id=500

Cc: Feng Tian <feng.tian@intel.com>
Cc: Michael Kinney <michael.d.kinney@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jeff Fan <jeff.fan@intel.com>
Reviewed-by: Feng Tian <feng.tian@intel.com>