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* support AVX512

* env DGL_CPU_INTEL_KERNEL_ENABLED=1

* env DGL_CPU_INTEL_KERNEL_LOG=1

* Add unittest test_spmm.cc
Co-authored-by: Izabela Mazur <izabela.mazur@intel.com>
Co-authored-by: Michal Szarmach <michal.szarmach@intel.com>

Review patch