xfs_repair: convert utility to use new rt extent helpers and types

xfs_repair: convert utility to use new rt extent helpers and types

Convert the repair program to use the new realtime extent types and
helper functions instead of open-coding them.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Bill O'Donnell <bodonnel@redhat.com>