xfs: fix EFI recovery livelocks

This series fixes a customer-reported transaction reservation bug
introduced ten years ago that could result in livelocks during log
recovery.  Log intent item recovery single-steps each step of a deferred
op chain, which means that each step only needs to allocate one
transaction's worth of space in the log, not an entire chain all at
once.  This single-stepping is critical to unpinning the log tail since
there's nobody else to do it for us.

This has been lightly tested with fstests.  Enjoy!

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
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