A stack can already be declared extern via K_KERNEL_STACK_EXTERN().
This adds similar macros for stack arrays.
Signed-off-by: Daniel Leung <daniel.leung@intel.com>
Moves Z_KERNEL_STACK_LEN() higher in the header file so it is
near the other stack size calculation macros. Also, it was
actually declared after it is first used in the header.
So this seems a logical move.
Signed-off-by: Daniel Leung <daniel.leung@intel.com>