net/mlx5: hw counters: Make fc_stats & fc_pool private

net/mlx5: hw counters: Make fc_stats & fc_pool private

The mlx5_fc_stats and mlx5_fc_pool structs are only used from
fs_counters.c. As such, make them private there.

mlx5_fc_pool is not used or referenced at all outside fs_counters.

mlx5_fc_stats is referenced from mlx5_core_dev, so instead of having it
as a direct member (which requires exporting it from fs_counters), store
a pointer to it, allocate it on init and clear it on destroy.
One caveat is that a simple container_of to get from a 'work' struct to
the outermost mlx5_core_dev struct directly no longer works, so an extra
pointer had to be added to mlx5_fc_stats back to the parent dev.

Signed-off-by: Cosmin Ratiu <cratiu@nvidia.com>
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Link: https://patch.msgid.link/20241001103709.58127-2-tariqt@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>