block, cfq: move icq cache management to block core

Let elevators set ->icq_size and ->icq_align in elevator_type and
elv_register() and elv_unregister() respectively create and destroy
kmem_cache for icq.

* elv_register() now can return failure.  All callers updated.

* icq caches are automatically named "ELVNAME_io_cq".

* cfq_slab_setup/kill() are collapsed into cfq_init/exit().

* While at it, minor indentation change for iosched_cfq.elevator_name
  for consistency.

This will help moving icq management to block core.  This doesn't
introduce any functional change.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/noop-iosched.c

@@ -94,9 +94,7 @@ static struct elevator_type elevator_noop = {
 
 static int __init noop_init(void)
 {
-	elv_register(&elevator_noop);
-
-	return 0;
+	return elv_register(&elevator_noop);
 }
 
 static void __exit noop_exit(void)