IB/mlx5: Move to fully dynamic UAR mode once user space supports it

Move to fully dynamic UAR mode once user space supports it.  In this case
we prevent any legacy mode of UARs on the allocated context and prevent
redundant allocation of the static ones.

Link: https://lore.kernel.org/r/20200324060143.1569116-6-leon@kernel.org
Signed-off-by: Yishai Hadas <yishaih@mellanox.com>
Reviewed-by: Michael Guralnik <michaelgur@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>