eventpoll: Use generic list for eventpoll files

Since eventpoll opening time is set by dependencies
(see epoll_not_ready_tfd()), we may safely store them
in generic list.

v4: New

Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>