Unify the QP memory allocation across different paths,
so it will be in one place.

Link: https://lore.kernel.org/r/20200427154636.381474-5-leon@kernel.orgReviewed-by: NMaor Gottlieb <maorg@mellanox.com>
Signed-off-by: NLeon Romanovsky <leonro@mellanox.com>
Signed-off-by: NJason Gunthorpe <jgg@mellanox.com>