net/mlx5e: Use non-XSK page allocator in SHAMPO

The SHAMPO flow is not compatible with XSK, it can call the page pool
allocator directly to save a branch.

mlx5e_page_alloc is removed, as it's no longer used in any flow.

Signed-off-by: Maxim Mikityanskiy <maximmi@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>