RDMA/rds: Remove FMR support for memory registration

Use FRWR method for memory registration by default and remove the ancient
and unsafe FMR method.

Link: https://lore.kernel.org/r/3-v3-f58e6669d5d3+2cf-fmr_removal_jgg@mellanox.com


Signed-off-by: Max Gurtovoy <maxg@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>