Something like this should take care of it in PHPMyAdmin. Go to the SQL tab for wp_posts and run the following command*:
UPDATE wp_posts SET ping_status = replace(ping_status, 'open', 'closed') WHERE post_type = 'attachment';
Or if you want to turn of pings/trackbacks for all posts, remove the WHERE statement at the end:
UPDATE wp_posts SET ping_status = replace(ping_status, 'open', 'closed');
*DISCLAIMER: Use at your own risk. Mucking around in PHPMyAdmin is an easy way to screw things up. It is advised that users test out changes on a non-production installation of WordPress (a test site) before using them on a live site. If you break something due to a typo in my command or negligence on your own part, don't come crying expecting sympathy.