Add support for mnist float model

Add mnist float model. As the entry function is different from others, a
field entry_func is added for the MlModel struct.

Change-Id: I485bf10f0756e2805636b77c4f9ba5bd1899c22e
diff --git a/samples/util/util.c b/samples/util/util.c
index d618534..655289a 100644
--- a/samples/util/util.c
+++ b/samples/util/util.c
@@ -98,11 +98,10 @@
   // Lookup the entry point function.
   // Note that we use the synchronous variant which operates on pure type/shape
   // erased buffers.
-  const char kMainFunctionName[] = "module.main";
   iree_vm_function_t main_function;
   if (iree_status_is_ok(result)) {
     result = (iree_vm_context_resolve_function(
-        context, iree_make_cstring_view(kMainFunctionName), &main_function));
+        context, iree_make_cstring_view(model->entry_func), &main_function));
   }
 
   // Prepare the input buffers.