kernel: Add stack_info to k_thread This patck adds the stack information into the k_thread data structure. The information will be set by when creating a new thread (_new_thread) and will be used by the scheduling process. Change-Id: Ibe79fe92a9ef8bce27bf8616d8e0c878508c267d Signed-off-by: Vincenzo Frascino <vincenzo.frascino@linaro.org>