IB/mlx5: Expose UAR object and its alloc/destroy commands

Expose UAR object and its alloc/destroy commands to be used over the ioctl
interface by user space applications.

This API supports both BF & NC modes and enables a dynamic allocation of
UARs once really needed.

As the number of driver objects were limited by the core ones when the
merged tree is prepared, had to decrease the number of core objects to
enable the new UAR object usage.

Link: https://lore.kernel.org/r/20200324060143.1569116-2-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>