RDMA/mlx5: Add support to get QP resource in RAW format

Add a generic function to use the resource dump mechanism to get the
QP resource data.

Link: https://lore.kernel.org/r/20200623113043.1228482-10-leon@kernel.org
Signed-off-by: Maor Gottlieb <maorg@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>