[CPU] Fix SDPA pattern matching (openvinotoolkit#23581)

### Details:
Limit the Concat layer to have maximum 3 children. The third one is
allowed to be a ShapeOf op only (to support Mixtral).

### Tickets:
 - 135375

Author: maxnick

src/plugins/intel_cpu/src/nodes/scaled_attn.cpp

@@ -1111,6 +1111,7 @@ void ScaledDotProductAttention::execute(dnnl::stream strm) {
         presentv_input = inputs[ID_VCACHE];
     } else {
         if (m_config.config.fuse_concat) {
+            CPU_NODE_ASSERT(m_k_state && m_v_state, "has null input states");
             // initialization will be also completed in this func
             gatherConcatPastkv(inputs[1], inputs[2], getSrcMemoryAtPort(orginSDPInputNumber));
 

src/plugins/intel_cpu/src/transformations/cpu_opset/common/pass/stateful_sdpa_fusion.cpp

@@ -108,8 +108,6 @@ StatefulSDPAFusion::StatefulSDPAFusion() {
 
         auto find_assign = [&](const ov::Output<ov::Node>& out, opset6::Assign*& assign, opset1::Convert*& cvt) {
             auto present_to = out.get_target_inputs();
-            if (present_to.size() < 2)
-                return false;
             for (auto& to : present_to) {
                 auto to_node = to.get_node();
                 if (auto convert = dynamic_cast<opset1::Convert*>(to_node)) {
@@ -149,6 +147,28 @@ StatefulSDPAFusion::StatefulSDPAFusion() {
         const auto concat_k_node = ov::as_type_ptr<opset6::Concat>(pattern_map.at(concat_k).get_node_shared_ptr());
         const auto concat_v_node = ov::as_type_ptr<opset6::Concat>(pattern_map.at(concat_v).get_node_shared_ptr());
 
+        for (auto&& item : {concat_k_node, concat_v_node}) {
+            auto&& children = item->get_output_target_inputs(0);
+            switch (children.size()) {
+                case 2:
+                    // pass, as the existence of Assign will be checked later
+                    break;
+                case 3:
+                    // the first one leads to SDPA, otherwise the matcher doesn't find the pattern
+                    // the second one leads to Assign, and this is checked later
+                    // the third child is allowed to be a ShapeOf op only, thus one of them must be ShapeOf
+                    if (!std::any_of(children.begin(), children.end(), [](const ov::Input<ov::Node>& child) {
+                            return ov::is_type<ov::op::v3::ShapeOf>(child.get_node()) ||
+                                ov::is_type<ov::op::v0::ShapeOf>(child.get_node());
+                        })) {
+                        return false;
+                    }
+                    break;
+                default:
+                    return false;
+            }
+        }
+
         opset6::Assign *assign_k_node = nullptr, *assign_v_node = nullptr;
         opset1::Convert *assign_cvt_k_node = nullptr, *assign_cvt_v_node = nullptr;
         if (!find_assign(concat_k_node, assign_k_node, assign_cvt_k_node))