net/mlx5: Remove unused fill page array API function

mlx5_fill_page_array API function is not used.
Remove it, reduce the number of exported functions.

Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Reviewed-by: Moshe Shemesh <moshe@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>