### What this PR does / why we need it?
Related to https://github.com/vllm-project/vllm-ascend/issues/4084
Implement multimodal_cpu_fields in model runner
- vLLM version: v0.12.0
- vLLM main:
ad32e3e19c
Signed-off-by: hfadzxy <starmoon_zhang@163.com>