xfs: support logging EFIs for realtime extents

xfs: support logging EFIs for realtime extents

Source kernel commit: 4c8900bbf106592ce647285e308abd2a7f080d88

Teach the EFI mechanism how to free realtime extents.  We're going to
need this to enforce proper ordering of operations when we enable
realtime rmap.

Declare a new log intent item type (XFS_LI_EFI_RT) and a separate defer
ops for rt extents.  This keeps the ondisk artifacts and processing code
completely separate between the rt and non-rt cases.  Hopefully this
will make it easier to debug filesystem problems.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>