[CI] Unifying Dockerfiles for ARM and X86 Builds (#21343)

Signed-off-by: Kebe <mail@kebe7jun.com>

docs/getting_started/installation/cpu/arm.inc.md

@@ -33,7 +33,7 @@ Testing has been conducted on AWS Graviton3 instances for compatibility.
 # --8<-- [end:pre-built-images]
 # --8<-- [start:build-image-from-source]
 ```bash
-docker build -f docker/Dockerfile.arm \
+docker build -f docker/Dockerfile.cpu \
         --tag vllm-cpu-env .
 
 # Launching OpenAI server