kernel: add architecture interface headers

include/sys/arch_inlines.h will contain all architecture APIs
that are used by public inline functions and macros,
with implementations deriving from include/arch/cpu.h.

kernel/include/arch_interface.h will contain everything
else, with implementations deriving from
arch/*/include/kernel_arch_func.h.

Instances of duplicate documentation for these APIs have been
removed; implementation details have been left in place.

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

include/kernel.h

@@ -5162,28 +5162,6 @@ extern void k_mem_domain_remove_thread(k_tid_t thread);
  */
 __syscall void k_str_out(char *c, size_t n);
 
-/**
- * @brief Start a numbered CPU on a MP-capable system
-
- * This starts and initializes a specific CPU.  The main thread on
- * startup is running on CPU zero, other processors are numbered
- * sequentially.  On return from this function, the CPU is known to
- * have begun operating and will enter the provided function.  Its
- * interrupts will be initialized but disabled such that irq_unlock()
- * with the provided key will work to enable them.
- *
- * Normally, in SMP mode this function will be called by the kernel
- * initialization and should not be used as a user API.  But it is
- * defined here for special-purpose apps which want Zephyr running on
- * one core and to use others for design-specific processing.
- *
- * @param cpu_num Integer number of the CPU
- * @param stack Stack memory for the CPU
- * @param sz Stack buffer size, in bytes
- * @param fn Function to begin running on the CPU.  First argument is
- *        an irq_unlock() key.
- * @param arg Untyped argument to be passed to "fn"
- */
 extern void z_arch_start_cpu(int cpu_num, k_thread_stack_t *stack, int sz,
 			    void (*fn)(int key, void *data), void *arg);