Add support for SHREGMAP+$mux, also fine tune $pmux
Add support for SHREGMAP+$mux, also fine tune $pmux

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