config.yml

services:
    entity_validator:
        class: Vendor\AppBundle\Entity\Validator
        arguments: [@validator]
        tags:
            - { name: doctrine.event_listener, event: prePersist }
            - { name: doctrine.event_listener, event: preUpdate }

Validator.php

<?php

namespace Vendor\AppBundle\Entity;

use Symfony\Component\Validator\Validator as SymfonyValidator;
use Doctrine\ORM\Event\LifecycleEventArgs;

class Validator {

    private $validator;

    function __construct(SymfonyValidator $validator) {
        $this->validator = $validator;
    }

    function __call($method, $args) {
        $entity = reset($args)->getEntity();
        $this->validator->validate($entity);        
    }
}