epoll: Add synchronous wakeup support for ep_poll_callback

[ Upstream commit 900bbaae67e980945dec74d36f8afe0de7556d5a ]

Now, the epoll only use wake_up() interface to wake up task.
However, sometimes, there are epoll users which want to use
the synchronous wakeup flag to hint the scheduler, such as
Android binder driver.
So add a wake_up_sync() define, and use the wake_up_sync()
when the sync is true in ep_poll_callback().

Co-developed-by: Jing Xia <jing.xia@unisoc.com>
Signed-off-by: Jing Xia <jing.xia@unisoc.com>
Signed-off-by: Xuewen Yan <xuewen.yan@unisoc.com>
Link: https://lore.kernel.org/r/20240426080548.8203-1-xuewen.yan@unisoc.com


Tested-by: Brian Geffon <bgeffon@google.com>
Reviewed-by: Brian Geffon <bgeffon@google.com>
Reported-by: Benoit Lize <lizeb@google.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
[ Redefine wake_up_sync(x) as __wake_up_sync(x, TASK_NORMAL, 1) to
  make it work on 5.4.y ]
Signed-off-by: Wenshan Lan <jetlan9@163.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>