Add bitwise $bweqx and $bwmux cells

The new bitwise case equality (`$bweqx`) and bitwise mux (`$bwmux`)
cells enable compact encoding and decoding of 3-valued logic signals
using multiple 2-valued signals.

techlibs/common/techmap.v

@@ -59,7 +59,7 @@ module _90_simplemap_compare_ops;
 endmodule
 
 (* techmap_simplemap *)
-(* techmap_celltype = "$pos $slice $concat $mux $tribuf $bmux" *)
+(* techmap_celltype = "$pos $slice $concat $mux $tribuf $bmux $bwmux $bweqx" *)
 module _90_simplemap_various;
 endmodule