Fixing GPTQ exllama kernel usage. (#1101)

# What does this PR do?

Fixes #1098 
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server/text_generation_server/utils/weights.py

@@ -212,7 +212,9 @@ def get_multi_weights_col(self, prefixes: List[str], quantize: str, dim: int):
                 g_idx = None
 
             bits, groupsize = self._get_gptq_params()
-            weight = (qweight, qzeros, scales, g_idx, bits, groupsize, False)
+            from text_generation_server.utils.layers import HAS_EXLLAMA
+            use_exllama = bits==4  and HAS_EXLLAMA and quantize == "gptq"
+            weight = (qweight, qzeros, scales, g_idx, bits, groupsize, use_exllama)
         else:
             w = [self.get_sharded(f"{p}.weight", dim=0) for p in prefixes]
             weight = torch.cat(w, dim=dim)