llama : load MTP tensors only if they are really used (#26296)

* llama : load MTP tensors only if they are really used

* llama : skip loading MTP (if not used) in remaining models that support MTP

---------

Co-authored-by: Stanisław Szymczyk <sszymczy@gmail.com>

src/llama-model.cpp

@@ -2390,6 +2390,7 @@ llama_model_params llama_model_default_params() {
         /*.use_extra_bufts             =*/ true,
         /*.no_host                     =*/ false,
         /*.no_alloc                    =*/ false,
+        /*.load_mtp                    =*/ false,
     };
 
     return result;