[AMD] Fail gracefully when AITER is unavailable gfx90a GPUs (#7187)

python/sglang/srt/layers/quantization/fp8.py

@@ -88,7 +88,7 @@ _is_fp8_fnuz = is_fp8_fnuz()
 _use_hip_int4 = get_bool_env_var("SGLANG_INT4_WEIGHT")
 _use_aiter = get_bool_env_var("SGLANG_USE_AITER") and _is_hip
 
-if _is_hip:
+if _is_hip and (_use_aiter or _use_hip_int4):
     from aiter import ActivationType, QuantType
     from aiter.fused_moe import fused_moe
     from aiter.fused_moe_bf16_asm import asm_moe, ck_moe_2stages