xilinx: improve specify for DSP48E1
xilinx: improve specify for DSP48E1

cliffordwolf/yosys,SymbiFlow/yosys,cliffordwolf/yosys,antmicro/yosys,YosysHQ/yosys,antmicro/yosys,SymbiFlow/yosys,antmicro/yosys,antmicro/yosys,SymbiFlow/yosys,cliffordwolf/yosys,YosysHQ/yosys,SymbiFlow/yosys,cliffordwolf/yosys,cliffordwolf/yosys,cliffordwolf/yosys,antmicro/yosys,SymbiFlow/yosys,SymbiFlow/yosys,antmicro/yosys,YosysHQ/yosys,YosysHQ/yosys,SymbiFlow/yosys,cliffordwolf/yosys,YosysHQ/yosys,antmicro/yosys,YosysHQ/yosys,cliffordwolf/yosys,SymbiFlow/yosys,cliffordwolf/yosys,YosysHQ/yosys,antmicro/yosys,YosysHQ/yosys