net/mlx5: Enable 4K UAR only when page size is bigger than 4K

When the page size isn't bigger than 4K, there is no added value of enabling 4K
UAR feature in the Firmware.

Modified the condition of enabling the 4K UAR accordingly.

Fixes: f502d834 ("net/mlx5: Activate support for 4K UARs")
Signed-off-by: Majd Dibbiny <majd@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>