RDMA/mlx5: Use new command interface API

DEVX can now use mlx5_cmd_do() which will not intercept the command
execution status and will provide full information of the return code.

DEVX can now propagate the error code safely to upper layers, to
indicate to the callers if the command was actually executed and the
error code indicates the command execution status availability in
the command outbox buffer.

Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: Artemy Kovalyov <artemyko@mellanox.com>
Reviewed-by: Yishai Hadas <yishaih@mellanox.com>
Reviewed-by: Moshe Shemesh <moshe@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>