sys/epoll: move the private handle to epoll_data_t

sync the struct epoll_event define with linux:

Linux Programmer's Manual:

DESCRIPTION

  EPOLL_CTL_DEL
    ...
       The event argument describes the object linked to the file descriptor
       fd.  The struct epoll_event is defined as:

           typedef union epoll_data {
               void        *ptr;
               int          fd;
               uint32_t     u32;
               uint64_t     u64;
           } epoll_data_t;

           struct epoll_event {
               uint32_t     events;      /* Epoll events */
               epoll_data_t data;        /* User data variable */
           };

https: //man7.org/linux/man-pages/man2/epoll_ctl.2.html

Change-Id: I3ad447b485fd331190e461a198ef7c39301eb1bb
Signed-off-by: chao.an <anchao@xiaomi.com>

include/sys/epoll.h

@@ -78,6 +78,7 @@ enum EPOLL_EVENTS
 
 typedef union poll_data
 {
+  FAR void    *ptr;      /* For use by drivers */
   int          fd;       /* The descriptor being polled */
 } epoll_data_t;
 
@@ -87,7 +88,6 @@ struct epoll_event
   FAR sem_t   *sem;      /* Pointer to semaphore used to post output event */
   pollevent_t  events;   /* The input event flags */
   pollevent_t  revents;  /* The output event flags */
-  FAR void    *priv;     /* For use by drivers */
 };
 
 struct epoll_head