UefiCpuPkg/MpInitLib: Keep compatible with former AP counting solution.

UefiCpuPkg/MpInitLib: Keep compatible with former AP counting solution.

For some special platforms (such as Ovmf), it is possible
that, some APs start up *and finish* before the remaining
APs start up *at all*. In this case, the enhance
solution by changes 0594ec41 not works as expected.

This change remove check CpuMpData->CpuCount logic to let old
solution still workable if platform owner still set a long
time for PcdCpuApInitTimeOutInMicroSeconds. It's platform
owner's response to decide which solution to use.

Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Jeff Fan <vanjeff_919@hotmail.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Eric Dong <eric.dong@intel.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jeff Fan <vanjeff_919@hotmail.com>