net/mlx5: DR, Expose an internal API to issue RDMA operations

Inserting or deleting a rule is done by RDMA read/write operation to SW
ICM device memory. This file provides the support for executing these
operations. It includes allocating the needed resources and providing an
API for writing steering entries to the memory.

Signed-off-by: Alex Vesker <valex@mellanox.com>
Signed-off-by: Mark Bloch <markb@mellanox.com>
Reviewed-by: Erez Shitrit <erezsh@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>