Add concat kernel for input fusions

src/targets/gpu/kernels/include/migraphx/kernels/concat.hpp

@@ -74,5 +74,22 @@ __device__ auto concat(Inputs... inputs)
     };
 }
 
+template <index_int Axis, class... InputPacks>
+__device__ auto concat2(InputPacks... input_packs)
+{
+    return [=](auto f, auto... ts) {
+        auto idx = make_index();
+        fold([&](auto start, auto input_pack) {
+            return input_pack([&](auto g, auto x, auto... xs) {
+                    concat_slices<Axis>(x, start, ts...)([&](auto z, auto... ys) {
+                        idx.global_stride(x.get_shape().elements(),
+                                        [&](auto i) { z[i] = f(g(x[i], xs[i]...), ys[i]...); });
+
+                    return start + concat_ends<Axis>(x);
+                });
+            });
+        })(_c<0>, input_packs...);
+}
+
 } // namespace migraphx
 #endif // MIGRAPHX_GUARD_KERNELS_CONCAT_HPP