jbd2: export jbd2_journal_[un]register_shrinker()

mainline inclusion
from mainline-5.14-rc1
commit 16aa4c9a
category: bugfix
bugzilla: 50788 https://gitee.com/openeuler/kernel/issues/I4DDEL
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=16aa4c9a1fbe763c147a964cdc1f5be8ed98ed13



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Export jbd2_journal_[un]register_shrinker() to fix this error when
ext4 is built as a module:

  ERROR: modpost: "jbd2_journal_unregister_shrinker" undefined!
  ERROR: modpost: "jbd2_journal_register_shrinker" undefined!

Fixes: 4ba3fcdd ("jbd2,ext4: add a shrinker to release checkpointed buffers")
Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20210630083638.140218-1-yi.zhang@huawei.com


Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Yang Erkun <yangerkun@huawei.com>
Signed-off-by: Chen Jun <chenjun102@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>