net/mlx5: use internal dma pools for frag buf alloc

net/mlx5: use internal dma pools for frag buf alloc

Add mlx5_dma_pool alloc/free paths, and wire mlx5_frag_buf allocation
and free paths to use them.

mlx5_frag_buf_alloc_node() now selects an mlx5_dma_pool to allocate
fragments from, instead of directly allocating full coherent pages.

mlx5_frag_buf_free() frees from the respective pool.

mlx5_dma_pool_alloc() keeps allocation fast by maintaining pages with
available indexes at the head of the list, so the common allocation path
can take a free index immediately. New backing pages are allocated only
when no free index is available.

mlx5_dma_pool_free() returns released indexes to the pool and frees a
backing page once all of its indexes become free. This avoids keeping
fully free pages for the lifetime of the pool and reduces coherent DMA
memory footprint.

Signed-off-by: Nimrod Oren <noren@nvidia.com>
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Link: https://patch.msgid.link/20260429201429.223809-4-tariqt@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>