xfs: clean up realtime type usage

The realtime code uses xfs_rtblock_t and xfs_fsblock_t in a lot of
places, and it's very confusing.  Clean up all the type usage so that an
xfs_rtblock_t is always a block within the realtime volume, an
xfs_fileoff_t is always a file offset within a realtime metadata file,
and an xfs_rtxnumber_t is always a rt extent within the realtime volume.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
-----BEGIN PGP SIGNATURE-----
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=osUy
-----END PGP SIGNATURE-----