Install vLLM from upstream as CPU backend was merged.

[xwu-intel]

vllm-project/vllm#3634

[carsonwang]

@xwu99 , except for the install script, is there anything else need to be updated? If not, can we update it as earliest?

[xwu-intel]

@xwu99 , except for the install script, is there anything else need to be updated? If not, can we update it as earliest?

sure, I will take it.