Add simulation models, techmap, and dfflegalize rules for Gowin DL-series latch primitives. Latches use the same physical BEL as DFFs with REGMODE set to LATCH. All 12 variants are supported: DL, DLE, DLN, DLNE, DLC, DLCE, DLNC, DLNCE, DLP, DLPE, DLNP, DLNPE.