IB/mlx5: Refactor UMR post send format

* Update struct mlx5_wqe_umr_ctrl_seg.
* Currenlty UMR send_flags aim only certain use cases: enabled/disable
  cached MR, modifying XLT for ODP. By making flags independent make UMR
  more flexible allowing arbitrary manipulations.
* Since different UMR formats have different entry sizes UMR request
  should receive exact size of translation table update instead of
  number of entries. Rename field npages to xlt_size in struct mlx5_umr_wr
  and update relevant code accordingly.
* Add support of length64 bit.

Signed-off-by: Artemy Kovalyov <artemyko@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>