Add zend opcache template to enable it

Add zend opcache template to enable it. This template is based on the opcache.ini in the php54-php-pecl-zendopcache-7.0.2-4.el6.x86_64.
@nak3 just to make sure... are you going to remove the `Requires:  php-pecl-opcache` line as well, right? Otherwise, the opcache.ini will be loaded from the system path.