[libj6] Move remaining j6 headers out of src/include

This means the kernel now depends on libj6. I've added the macro
definition __j6kernel when building for the kernel target, so I can
remove parts with #ifdefs.

src/kernel/kernel.module

@@ -6,7 +6,7 @@ kernel = module("kernel",
     output = "jsix.elf",
     targets = [ "kernel" ],
     description = "jsix kernel",
-    deps = [ "util", "cpu", "bootproto" ],
+    deps = [ "util", "cpu", "bootproto", "j6" ],
     includes = [ "." ],
     sources = [
         "apic.cpp",

src/kernel/memory_bootstrap.cpp

@@ -2,7 +2,6 @@
 
 #include <arch/memory.h>
 #include <bootproto/kernel.h>
-#include <j6/init.h>
 #include <util/no_construct.h>
 
 #include "assert.h"

src/kernel/scheduler.cpp

@@ -1,6 +1,5 @@
 #include <stddef.h>
 
-#include <j6/init.h>
 #include <util/spinlock.h>
 
 #include "apic.h"