Predictor not support multi-gpu

[yslin1995]

The predictor seems only support single gpu inference: https://github.com/alibaba/EasyNLP/blob/cda9b42358156afed3a0e27173d5e48ef32f0686/easynlp/core/predictor.py#L130

but the trainer supports multi-gpu training: https://github.com/alibaba/EasyNLP/blob/01fef50c3cda57971de2764b9095a152b1300a9e/easynlp/core/trainer.py#L96

Is there any plan for supporting multi-gpu inference?

[yslin1995]

@minghui