xfs_repair: support more than 2^32 owners per physical block

xfs_repair: support more than 2^32 owners per physical block

Now that the incore structures handle more than 2^32 records correctly,
fix the refcountbt generation code to handle the case of that many rmap
records pointing to a piece of space in an AG.  This fixes the problem
where the refcountbt cannot be rebuilt properly because of integer
truncation if there are more than 4.3 billion owners of a piece of
space.

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