[LLM] Move embedding layer to CPU for iGPU inference (#9343)

* Move embedding layer to CPU for iGPU llm inference

* Empty cache after to cpu

* Remove empty cache as it seems to have some negative effect to first token

python/llm/src/bigdl/llm/transformers/embedding.py

@@ -21,5 +21,6 @@ from torch import Tensor
 
 class LLMEmbedding(torch.nn.Embedding):
     def forward(self, x: Tensor):
-        x_shape = x.shape
-        return self.weight[x.reshape(-1)].reshape(*x_shape, -1)
+        if self.weight.device != 'cpu':
+            self.to('cpu')
+        return super().forward(x.to('cpu')).to(x.device)