Makes it easier to handle init vs core cleanly, though the change is
fairly invasive across random architectures.

It simplifies the rbtree code immediately, however, while keeping the
core data together in the same cachline (now iff the rbtree code is
enabled).
Acked-by: NPeter Zijlstra <peterz@infradead.org>
Reviewed-by: NJosh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: NRusty Russell <rusty@rustcorp.com.au>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>