net/mlx5: add device configuration structure

net/mlx5: add device configuration structure

Move device configuration and features capabilities to its own structure.
This structure is filled by mlx5_pci_probe(), outside of this function
it should be treated as *read only*.

This configuration struct will be used for the Tx/Rx queue setup to
select the Tx/Rx queue parameters based on the user configuration and
device capabilities.
In addition it will be used by the burst selection function to decide
on the best pkt burst to be used.

Signed-off-by: Shahaf Shuler <shahafs@mellanox.com>
Signed-off-by: Nelio Laranjeiro <nelio.laranjeiro@6wind.com>