io_uring: move poll handling into its own file

Add a io_poll_issue() rather than export the general task_work locking
and io_issue_sqe(), and put the io_op_defs definition and structure into
a separate header file so that poll can use it.

Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: axboe

io_uring/Makefile

@@ -6,5 +6,5 @@ obj-$(CONFIG_IO_URING)		+= io_uring.o xattr.o nop.o fs.o splice.o \
 					sync.o advise.o filetable.o \
 					openclose.o uring_cmd.o epoll.o \
 					statx.o net.o msg_ring.o timeout.o \
-					sqpoll.o fdinfo.o tctx.o
+					sqpoll.o fdinfo.o tctx.o poll.o
 obj-$(CONFIG_IO_WQ)		+= io-wq.o