xfs: support recovering rmap intent items targetting realtime extents

xfs: support recovering rmap intent items targetting realtime extents

Now that we have rmap on the realtime device and rmap intent items that
target the realtime device, log recovery has to support remapping
extents on the realtime volume.  Make this work.  Identify rtrmapbt
blocks in the log correctly so that we can validate them during log
recovery.

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