UefiCpuPkg/MpInitLib: Make sure AP uses correct StartupApSignal

UefiCpuPkg/MpInitLib: Make sure AP uses correct StartupApSignal

Every processor's StartupApSignal is initialized in
MpInitLibInitialize() before calling CollectProcessorCount().
When SortApicId() is called from CollectProcessorCount(), AP Index
is re-assigned by APIC ID. But SortApicId() forgets to set the
correct StartupApSignal when sorting the AP.

The patch fixes this issue.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Star Zeng <star.zeng@intel.com>
Signed-off-by: Ruiyu Ni <ruiyu.ni@intel.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>
Cc: Chasel Chiu <chasel.chiu@intel.com>