RDMA/mlx5: Move DRIVER QP flags check into separate function

Perform validation of DRIVER QP in relevant function.

Link: https://lore.kernel.org/r/20200427154636.381474-11-leon@kernel.org


Reviewed-by: Maor Gottlieb <maorg@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>