btrfs: separate types for submit_bio_start and submit_bio_done

The callbacks make use of different parameters that are passed to the
other type unnecessarily. This patch adds separate types for each and
the unused parameters will be removed.

The type extent_submit_bio_hook_t keeps all parameters and can be used
where the start/done types are not appropriate.

Signed-off-by: David Sterba <dsterba@suse.com>