[Test] start adding eltwise op test

tests/fpgadataflow/test_fpgadataflow_eltwise.py

+import numpy as np
+import onnx.parser as oprs
+import qonnx.core.data_layout as dl
+from qonnx.core.datatype import DataType
+from qonnx.core.modelwrapper import ModelWrapper
+from qonnx.transformation.infer_shapes import InferShapes
+
+import finn.transformation.fpgadataflow.convert_to_hls_layers as to_hls
+
+
+def build_model(dt0, dt1):
+    np.random.seed(0)
+    shp = [1, 3, 4, 2]
+    shp_str = str(shp)
+    input = f"""
+    <
+        ir_version: 7,
+        opset_import: ["" : 9]
+    >
+    agraph (float{shp_str} in0, float{shp_str} in1) => (float{shp_str} out0)
+    {{
+        sub_out = Sub(in0, in1)
+        out0 = Abs(sub_out)
+    }}
+    """
+    model = oprs.parse_model(input)
+    model = ModelWrapper(model)
+    model.set_tensor_datatype("in0", dt0)
+    model.set_tensor_datatype("in1", dt1)
+    model.set_tensor_layout("in0", dl.NHWC)
+    model.set_tensor_layout("in1", dl.NHWC)
+    model = model.transform(InferShapes())
+    return model
+
+
+def test_fpgadataflow_eltwise():
+    dt0 = DataType["UINT7"]
+    dt1 = DataType["UINT8"]
+    model = build_model(dt0, dt1)
+    model = model.transform(to_hls.InferStreamingEltwiseAbsDiff())
+    assert len(model.graph.node) == 1
+    assert model.graph.node[0].op_type == "StreamingEltwise"