UefiCpuPkg/MpInitLib: wait no longer than necessary for initial AP startup

UefiCpuPkg/MpInitLib: wait no longer than necessary for initial AP startup

Sometimes a platform knows exactly how many CPUs it has at boot. It should
be able to
- set PcdCpuMaxLogicalProcessorNumber dynamically to this number,
- set PcdCpuApInitTimeOutInMicroSeconds to a very long time (for example
  MAX_UINT32, approx. 71 minutes),
- and expect that MpInitLib wait exactly as long as necessary for all APs
  to report in.

Other platforms should be able to continue setting a reasonably large
upper bound on supported CPUs, and waiting for a reasonable, fixed amount
of time for all APs to report in.

Add this functionality. The TimedWaitForApFinish() function will return
when all APs have reported in, or the timeout has expired -- whichever
happens first.

(Accessing these PCDs dynamically is safe. The PEI and DXE phase instances
of this library are restricted to PEIM and DXE_DRIVER client modules, thus
the PCD accesses cannot be linked into runtime code.)

Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Jeff Fan <jeff.fan@intel.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Michael Kinney <michael.d.kinney@intel.com>
Bugzilla: https://bugzilla.tianocore.org/show_bug.cgi?id=116
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Jeff Fan <jeff.fan@intel.com>