UefiCpuPkg/CpuCacheInfoLib: Support no enabled AP case in DxeLib

UefiCpuPkg/CpuCacheInfoLib: Support no enabled AP case in DxeLib

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=3195

Support system has no enabled AP case in DxeCpuCacheInfoLib.
Otherwise, if the system only has 1 BSP without any enabled AP,
UEFI POST hangs when invoking StartupAllAPs protocol because
EFI_NOT_STARTED is returned.

Signed-off-by: Jason Lou <yun.lou@intel.com>
Reviewed-by: Ray Ni <ray.ni@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Rahul Kumar <rahul1.kumar@intel.com>