xfs: factor out xfs_defer_pending_abort

Factor out xfs_defer_pending_abort() from xfs_defer_trans_abort(), which
not use transaction parameter, so it can be used after the transaction
life cycle.

Signed-off-by: Long Li <leo.lilong@huawei.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Chandan Babu R <chandanbabu@kernel.org>