[Feature] 给 lmdeploy pytorch引擎，添加一个权重参数加载精度的参数。

### Motivation

## 硬件 T4 ，16G
## 需求：
给pytorch添加一个加载精度的参数，类似：vllm 的 dtype = [--dtype {auto,half,float16,bfloat16,float,float32}] ，让用户可以主动根据硬件能力选择 加载/推理 精度。

### 命令
lmdeploy serve api_server Qwen/Qwen1.5-1.8B-Chat --server-port 23333 --cache-max-entry-count 0.5

### 错误
2024-04-06 01:12:36,466 - lmdeploy - ERROR - AssertionError: bf16 is not supported on your device
2024-04-06 01:12:36,466 - lmdeploy - ERROR - test failed!
Your device does not support `torch.bfloat16`. Try edit `torch_dtype` in `config.json`.
Note that this might have negative effect!

### Related resources

_No response_

### Additional context

_No response_