kernel: add arch interface for idle functions

k_cpu_idle() and k_cpu_atomic_idle() were being directly
implemented by arch code.

Rename these implementations to z_arch_cpu_idle() and
z_arch_cpu_atomic_idle(), and call them from new inline
function definitions in kernel.h.

Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>
20 files changed