0329fad927
### What this PR does / why we need it? Deepseek v3 now adopt vanilla chunked prefill on MLA part which is ineffcient for computing but necessary for chunked prefill. Since PR https://github.com/vllm-project/vllm-ascend/pull/543 bring v0 scheduler into vllm-ascend, we can now adopt torch_npu._npu_flash_attention inside the mla backend for more performance boost. Also there are some redundant computation inside the rope, which is also removed. This PR should bring some performance gain for deepseek eager mode inference. --------- Signed-off-by: ganyi <pleaplusone.gy@gmail.com>