Currently we have the add/del functions generic so that we can use them
for both extent buffers and extent states.  We want to separate this
code however, so separate these helpers into per-object helpers in
anticipation of the split.
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>