kernel: separate headers into kernel and user headers

all kernel headers have been moved from include/mango to include/kernel
and include definitions that are only relevant to kernel-space.

any definitions that are relevant to both kernel- and user-space
(i.e. type definitions, syscall IDs) have been moved to
include/mango within libmango.

vm/vm-object.c

@@ -1,5 +1,6 @@
-#include <mango/printk.h>
-#include <mango/vm-object.h>
+#include <kernel/printk.h>
+#include <kernel/util.h>
+#include <kernel/vm-object.h>
 
 #define VM_OBJECT_CAST(p)                                                      \
 	OBJECT_C_CAST(struct vm_object, vo_base, &vm_object_type, p)