Re-enable Arm CPU vLLM HUD Benchmarks

[fadara01]

• re-enables the benchmarks disabled in Several minor tweak to vllm benchmark workflow #114
• related to Enable aarch64 CPU performance benchmarks vllm-project/vllm#26494 (not sure which needs to go in first)
• use default block_size in serving benchmarks (i.e. 128 instead of setting it to 16)
• uses ON_CPU=1 for both Arm & Intel, which mirrors the corresponding script we call in vLLM.