DDR2 model and testbench

DDR2modelandtestbench，MicronDDR2die；FileDescriptions:------------------ddr2.v-ddr2modelddr2_mcp.v-structuralwrapperforddr2-multi-chippackagemodelddr2_module.v-structuralwrapperforddr2-modulemodelddr2_parameters.vh-filethatcontainsallparametersusedbythemodelreadme.t