RDMA/mlx5: Rework custom driver QP type creation

Starting from commit 2b1f7470 ("RDMA/core: Allow drivers to disable
restrack DB") the restrack is able to handle non-standard QP types either.

That change allows us to rewrite custom QP calls to their IB/core
counterparts, so we will use general QP creation flow even for the driver
QP types.

Link: https://lore.kernel.org/r/51682ab82298748941f38bd23ee3bf77ef1cab7b.1627040189.git.leonro@nvidia.com


Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>