[FP8][Kernel] Dynamic kv cache scaling factors computation (#11906)

Signed-off-by: Gregory Shtrasberg <Gregory.Shtrasberg@amd.com>
Co-authored-by: Micah Williamson <micah.williamson@amd.com>

vllm/v1/attention/backends/flash_attn.py

@@ -166,10 +166,6 @@ class FlashAttentionImpl(AttentionImpl):
         Returns:
             shape = [num_tokens, num_heads * head_size]
         """
-        # NOTE(woosuk): FlashAttention does not support FP8 KV cache.
-        assert layer._k_scale == 1.0 and layer._v_scale == 1.0, (
-            "key/v_scale is not supported in FlashAttention.")
-
         assert output is not None, "Output tensor must be provided."
 
         if attn_metadata is None: