[Refactor]unify calls to torch_npu.npu_mla_prolog_v3 (#14676)

### What this PR does / why we need it?
torchNPU provide the API(npu_mla_prolog_v3) which support MLA
operations, while the legacy _C_ascend.mla_preprocess operator provide
the same function. we would like to remove the _C_ascend.mla_preprocess
operator in the vllm_ascend
### Does this PR introduce _any_ user-facing change?
NONE
### How was this patch tested?
UT
the testcase test_process_weights_for_fused_mlapo is modified to adpate
the PR, which unified the mock function and divided to two
cases(test_process_weights_for_fused_mlapo and
test_process_weights_for_fused_mlapo_with_fa_quant)
Function test
test environment
Model :/mnt/weight/DeepSeek-V3.1-w4a8-perchannle
Hardware: 8 x A3 Ascend910 NPU Card
export OMP_NUM_THREADS=100
export OMP_PROC_BIND=false
export HCCL_BUFFSIZE=1024
export VLLM_RPC_TIMEOUT=3600000
export VLLM_EXECUTE_MODEL_TIMEOUT_SECONDS=3600000
export VLLM_ENGINE_READY_TIMEOUT_S=7200
export VLLM_ASCEND_ENABLE_MLAPO=1
test result
performance: GSMK8K success:100%(120/120) output tps:150(tota) output
tps:18.77(per card) E2E tps:300.62
TTFT:345639.9TPOT:181.7ms
precision: GSMK8K : 96.51%（输出长度32768
temperature 1， top_p 0.95） GPQA: 74.24% （输出长度65536temperature 1， top_p
0.95）

- vLLM version: v0.27.1
- vLLM main:
https://github.com/vllm-project/vllm/commit/ba07e4a48fc951300d97eb506217dd530583dea3

Signed-off-by: luomin2005 <icecool.luomin@huawei.com>