kernel: Fix nano_internal.h inclusion

_Swap() is defined in nano_internal.h.  Everything calls _Swap().
Pretty much nothing that called _Swap() included nano_internal.h,
expecting it to be picked up automatically through other headers (as
it happened, from the kernel arch-specific include file).  A new
_Swap() is going to need some other symbols in the inline definition,
so I needed to break that cycle.  Now nothing sees _Swap() defined
anymore.  Put nano_internal.h everywhere it's needed.

Our kernel includes remain a big awful yucky mess.  This makes things
more correct but no less ugly.  Needs cleanup.

Signed-off-by: Andy Ross <andrew.j.ross@intel.com>

kernel/mem_slab.c

@@ -13,6 +13,7 @@
 #include <misc/dlist.h>
 #include <ksched.h>
 #include <init.h>
+#include <nano_internal.h>
 
 extern struct k_mem_slab _k_mem_slab_list_start[];
 extern struct k_mem_slab _k_mem_slab_list_end[];