kernel: refactor thread_monitor_init into common code

We do the same thing on all arch's right now for thread_monitor_init so
lets put it in a common place.  This also should fix an issue on xtensa
when thread monitor can be enabled (reference to _nanokernel.threads).

Change-Id: If2f26c1578aa1f18565a530de4880ae7bd5a0da2
Signed-off-by: Kumar Gala <kumar.gala@linaro.org>
7 files changed