jbd2: move load_superblock() dependent functions

jbd2: move load_superblock() dependent functions

Move load_superblock() declaration and the functions it calls before
journal_init_common(). This is a preparation for moving a call to
load_superblock() from jbd2_journal_load() and jbd2_journal_wipe() to
journal_init_common(). No functional changes.

Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20230811063610.2980059-2-yi.zhang@huaweicloud.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>