Vlv2TbltDevicePkg/PpmPolicy: Fix call to MP Services Protocol

Vlv2TbltDevicePkg/PpmPolicy: Fix call to MP Services Protocol

The NumberOfEnabledProcessors parameter to the MP Services
Protocol service GetNumberOfProcessors() is not optional and is
not allowed to be NULL.  Add the CpuEnabledCount local variable
and pass it into GetNumberOfProcessors().

Cc: Zailiang Sun <zailiang.sun@intel.com>
Cc: Yi Qian <yi.qian@intel.com>
Signed-off-by: Michael D Kinney <michael.d.kinney@intel.com>
Reviewed-by: Zailiang Sun <zailiang.sun@intel.com>
Reviewed-by: Yi Qian <yi.qian@intel.com>