layers:Check all memory bindings

There are a few places in the code where we assume that an image or
buffer doesn't have a sparse binding. These cases break with sparse
bindings.

To fix I added a function to BINDING class to retrieve all memory
bindings and then updated a few spots with bad assumption to make use
of this new GetBoundMemory() function.
diff --git a/layers/descriptor_sets.cpp b/layers/descriptor_sets.cpp
index d231543..4d06845 100644
--- a/layers/descriptor_sets.cpp
+++ b/layers/descriptor_sets.cpp
@@ -406,14 +406,15 @@
                             *error = error_str.str();
                             return false;
                         } else {
-                            auto mem_entry = getMemObjInfo(device_data_, buffer_node->binding.mem);
-                            if (!mem_entry) {
-                                std::stringstream error_str;
-                                error_str << "Descriptor in binding #" << binding << " at global descriptor index " << i
-                                          << " uses buffer " << buffer << " that references invalid memory "
-                                          << buffer_node->binding.mem << ".";
-                                *error = error_str.str();
-                                return false;
+                            for (auto mem_binding : buffer_node->GetBoundMemory()) {
+                                if (!getMemObjInfo(device_data_, mem_binding)) {
+                                    std::stringstream error_str;
+                                    error_str << "Descriptor in binding #" << binding << " at global descriptor index " << i
+                                              << " uses buffer " << buffer << " that references invalid memory " << mem_binding
+                                              << ".";
+                                    *error = error_str.str();
+                                    return false;
+                                }
                             }
                         }
                         if (descriptors_[i]->IsDynamic()) {