UefiCpuPkg RegisterCpuFeaturesLib: Fix an ASSERTION issue

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=1968

We met assertion like below, it happens when there is only
one processor.

ASSERT_EFI_ERROR (Status = Not started)
ASSERT [CpuFeaturesDxe] X:\XXX\XXX\RegisterCpuFeaturesLib\
  DxeRegisterCpuFeaturesLib.c(149): !EFI_ERROR (Status)

The code should not call StartupAllAPs when there is only one processor.

Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Eric Dong <eric.dong@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Cc: Chandana Kumar <chandana.c.kumar@intel.com>
Cc: Kevin Li <kevin.y.li@intel.com>
Signed-off-by: Star Zeng <star.zeng@intel.com>
Reviewed-by: Eric Dong <eric.dong@intel.com>

UefiCpuPkg/Library/RegisterCpuFeaturesLib/CpuFeaturesInitialize.c

@@ -1071,10 +1071,12 @@ CpuFeaturesDetect (
 
   CpuInitDataInitialize ();
 
-  //
-  // Wakeup all APs for data collection.
-  //
-  StartupAPsWorker (CollectProcessorData, NULL);
+  if (CpuFeaturesData->NumberOfCpus > 1) {
+    //
+    // Wakeup all APs for data collection.
+    //
+    StartupAPsWorker (CollectProcessorData, NULL);
+  }
 
   //
   // Collect data on BSP