fix[ROCm]: Remove unconditional aiter import (#32902)

Signed-off-by: rabi <ramishra@redhat.com>

vllm/v1/attention/backends/rocm_aiter_fa.py

@@ -32,10 +32,11 @@ from vllm.v1.kv_cache_interface import AttentionSpec
 _PARTITION_SIZE_ROCM = 256
 _CP_TOKENS_PER_ITER_ROCM = 32 * 1024
 if current_platform.is_rocm():
-    import aiter
-
     from vllm.triton_utils import tl, triton
 
+    if rocm_aiter_ops.is_enabled():
+        import aiter
+
     def block_size(x, head_dim):
         return min(65536 // x.element_size(), triton.next_power_of_2(head_dim))