Point to NVIDIA documentation for device specific information now that the
Mellanox documentation site is deprecated. Refer to kernel documentation
sources for generic information not specific to mlx5 devices.

Signed-off-by: Rahul Rameshbabu <rrameshbabu@nvidia.com>
Reviewed-by: Gal Pressman <gal@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>