kernel: Introduce k_work_poll

This commit adds new k_work_poll interface. It allows to
submit given work to a workqueue automatically when one of the
watched pollable objects changes its state.

Signed-off-by: Piotr Zięcik <piotr.ziecik@nordicsemi.no>
Signed-off-by: Peter A. Bigot <pab@pabigot.com>