UefiCpuPkg/MpInitLib: Enhance waiting for AP initialization logic.

UefiCpuPkg/MpInitLib: Enhance waiting for AP initialization logic.

Current logic always waiting for a specific value to collect all APs
count. This logic may caused some platforms cost too much time to
wait for time out.
This patch add new logic to collect APs count. It adds new variable
NumApsExecuting to detect whether all APs have finished initialization.
Each AP let NumApsExecuting++ when begin to initialize itself and let
NumApsExecuting-- when it finish the initialization. BSP base on whether
NumApsExecuting == 0  to finished the collect AP process.

Cc: Ruiyu Ni <ruiyu.ni@intel.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: Jeff Fan <vanjeff_919@hotmail.com>