LU-15399 llite: dont restart directIO with IOCB_NOWAIT

LU-15399 llite: dont restart directIO with IOCB_NOWAIT

It should hanlde FLR mirror retry and io_uring with IOCB_NOWAIT
flag differently.

int cl_io_loop(const struct lu_env *env, struct cl_io *io)
{
	...
	if (result == -EAGAIN && io->ci_ndelay) {
		io->ci_need_restart = 1;
		result = 0;
	}
	...
}

ssize_t
generic_file_read_iter(struct kiocb *iocb, struct iov_iter *iter)
{
	...
	if (iocb->ki_flags & IOCB_NOWAIT) {
		if (filemap_range_has_page(mapping, iocb->ki_pos,
					   iocb->ki_pos +
					   count - 1))
			return -EAGAIN;
	...
}

In current code, it will restart I/O engine for read when get
-EAGAIN code.
However, for io_uring direct IO with IOCB_NOWAIT, if found that
there are cache pages in the current I/O range, it should return
-EAGAIN to the upper layer immediately. Otherwise, it will stuck
in an endless loop.

This patch also adds a tool "io_uring_probe" to check whether
the kernel supports io_uring fully.
The reason adding this check is because the rhel8.5 kernel has
backported io_uring:
cat /proc/kallsyms |grep io_uring
ffffffffa8510e10 W __x64_sys_io_uring_enter
ffffffffa8510e10 W __x64_sys_io_uring_register
ffffffffa8510e10 W __x64_sys_io_uring_setup
but the io_uring syscalls return -ENOSYS.

Test-Parameters: clientdistro=ubuntu2004 testlist=sanity-pcc
Signed-off-by: Qian Yingjin <qian@ddn.com>
Change-Id: Id4374382e56e90d02349676891aa57b216b3deff