xfs_repair: move common dir2 and attr_repair code to da_util.c

xfs_repair: move common dir2 and attr_repair code to da_util.c

Now that dir2.c and attr_repair.c are functionally identical,
move the duplicate code into a new file da_util.c, with da_util.h
as a header file for the common functions.

Last step will be to fix up comments and printfs' to be appropriate
for code that checks both dirs and attrs.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>