Since all mlx4 QP have same storage type, move the QP allocation to be in
one place. This change is preparation to removal of such allocation from
the driver.

Link: https://lore.kernel.org/r/20200926102450.2966017-7-leon@kernel.orgReviewed-by: Maor Gottlieb <maorg@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>