[GPU] do not need to broadcast for eltwise post ops constant argument…

… in onednn gemm (openvinotoolkit#27671)

### Details:
- observe huge perf drop with onednn binary-ops per tensor mode (e.g.
per_tensor POLICY input or integer 15 input)):


![image](https://github.com/user-attachments/assets/1d71f89b-2ec5-4afa-8f2d-b349ce7f8a49)

in this model, the argument of the binary is constant, but it has been
broadcasted to match the gemm output tensor layout, yet it leads to huge
perf drop

- remove the unecessary broadcast for scalar argument which is later
feed to onednn binary ops

### Tickets:
 - 152186

---------

Signed-off-by: fishbell <[email protected]>

src/plugins/intel_gpu/src/graph/graph_optimizer/reorder_inputs.cpp

@@ -1003,6 +1003,10 @@ void reorder_inputs::run(program& p, reorder_factory& rf) {
                     if (gemm_dims[0] == data_dims[0])
                         continue;
 
+                    auto data_shape = data_layout.get_shape();
+                    if (data_shape.size() && shape_size(data_shape) == 1ul)
+                        continue;
+
                     static size_t idx = 0;
                     const auto prim_id = "broadcast:" + data.id() + "_broadcasted" + std::to_string(idx++);
                     auto broadcast_prim = std::make_shared<cldnn::broadcast>(prim_id, cldnn::input_info(data.id()), gemm_layout.get_shape(),

src/plugins/intel_gpu/tests/unit/fusions/gemm_fusion_test.cpp

@@ -398,6 +398,36 @@ TEST_P(gemm_2in_add, eltwise_postop_cached) {
     execute(p, false, true);
 }
 
+TEST_P(gemm_2in_add, eltwise_postop_scalar) {
+    auto p = GetParam();
+
+    if (engine.get_device_info().supports_immad) {
+        ov::intel_gpu::ImplementationDesc gemmv_impl = { cldnn::format::type::any, "", impl_types::onednn };
+        cfg_fused.set_property(ov::intel_gpu::force_implementations(ov::intel_gpu::ImplForcingMap{ { "gemm_prim", gemmv_impl } }));
+    }
+
+    auto add_data_layout = get_output_layout(p);
+    auto add_data_size = add_data_layout.get_partial_shape();
+    for (size_t i = 0; i < add_data_size.size(); i++)
+        add_data_size[i] = 1;
+    add_data_layout.set_partial_shape(add_data_size);
+
+    auto in_layout0 = get_input_layout(p, 0);
+    auto in_layout1 = get_input_layout(p, 1);
+
+    create_topologies(
+        input_layout("input0", in_layout0),
+        input_layout("input1", in_layout1),
+        data("add_data", get_mem(add_data_layout, 0.5f)),
+        gemm("gemm_prim", { input_info("input0"), input_info("input1") }, data_types::f32, false, false, 1.f, 0.f, in_layout0.get_rank(), in_layout1.get_rank()),
+        eltwise("add_prim", { input_info("gemm_prim"), input_info("add_data") }, p.eltwise_m, p.default_type),
+        reorder("reorder_bfyx", input_info("add_prim"), p.default_format, data_types::f32)
+    );
+
+    tolerance = default_tolerance(p.default_type);
+    execute(p, false, true);
+}
+
 INSTANTIATE_TEST_SUITE_P(fusings_gpu, gemm_2in_add, ::testing::ValuesIn(std::vector<gemm_test_params>{
     // gemm_test_params{ CASE_GEMM_2IN_FP16_3, 3, 4, "", broadcast_kinds::none, eltwise_mode::sum },    // TODO: check why failed in eltwise_postop_dynamic
     gemm_test_params{ CASE_GEMM_2IN_FP16_4, 3, 4, "", broadcast_kinds::none, eltwise_mode::sum },