Returns the default form state for the given entity and operation.
EntityInterface $entity: The entity to be created or edited.
$operation: (optional) The operation identifying the form to be processed.
A $form_state array already filled the entity form controller.
function entity_form_state_defaults(EntityInterface $entity, $operation = 'default') {
$form_state = array();
$controller = Drupal::entityManager()
->getFormController($entity
->entityType(), $operation);
$controller
->setEntity($entity);
$form_state['build_info']['callback_object'] = $controller;
$form_state['build_info']['base_form_id'] = $controller
->getBaseFormID();
$form_state['build_info']['args'] = array();
return $form_state;
}