xfs: make file range exchange support realtime files

xfs: make file range exchange support realtime files

Source kernel commit: e62941103faa2eedba6a155316e059a490c743a6

Now that bmap items support the realtime device, we can add the
necessary pieces to the file range exchange code to support exchanging
mappings.  All we really need to do here is adjust the blockcount
upwards to the end of the rt extent and remove the inode checks.

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