IB/mlx5: Support 4k UAR for libmlx5

Add fields to structs to convey to kernel an indication whether the
library supports multi UARs per page and return to the library the size
of a UAR based on the queried value.

Signed-off-by: Eli Cohen <eli@mellanox.com>
Reviewed-by: Matan Barak <matanb@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>