Data corruption has been seen with Mellanox SRP targets when FMRs
create a memory region with I/O virtual address != 0.  Add a
workaround that disables FMR merging for Mellanox targets (OUI 0002c9).
Signed-off-by: NIshai Rabinovitz <ishai@mellanox.co.il>
Signed-off-by: NMichael S. Tsirkin <mst@mellanox.co.il>
Signed-off-by: NRoland Dreier <rolandd@cisco.com>