Supply a decidate thread, which can moniter a set of fds with epoll,
when the data is ready, call the corresponding callback.
This iothread will be created automatically with the first successful
call to iothread_add, and will be destroyed in iothread_deinit if it
was created.
Note, currenlty only support one iothread.
Tracked-On: #7940
Signed-off-by: Conghui <conghui.chen@intel.com>
Acked-by: Wang, Yu1 <yu1.wang@intel.com>
