xfs: refactor log recovery item sorting into a generic dispatch structure

xfs: refactor log recovery item sorting into a generic dispatch structure

Source kernel commit: 86ffa471d9ce6ac3fda66f704c3143c3d55181f5

Create a generic dispatch structure to delegate recovery of different
log item types into various code modules.  This will enable us to move
code specific to a particular log item type out of xfs_log_recover.c and
into the log item source.

The first operation we virtualize is the log item sorting.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Chandan Babu R <chandanrlinux@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>