mlx5: Fix missing device local_dma_lkey

The mlx5 driver exposes device capability IB_DEVICE_LOCAL_DMA_LKEY
but does not set the the device local_dma_lkey. This breaks
rpcrdma drivers.

Query and set this lkey when creating the device resources.

Signed-off-by: Sagi Grimberg <sagig@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>