Add Mellanox to lust of copyright holders and replace copyright
boilerplate with relevant SPDX tag.

Link: https://lore.kernel.org/r/20191020071559.9743-4-leon@kernel.orgSigned-off-by: Leon Romanovsky <leonro@mellanox.com>
Reviewed-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>