Improvements in muxcover
Improvements in muxcover

- Slightly under-estimate cost of decoder muxes
- Prefer larger muxes at tree root at same cost
- Don't double-count input cost for partial muxes
- Add debug log output

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