net/mlx5e: kTLS, Add debugfs

Add TLS debugfs to improve observability by exposing the size of the tls
TX pool.

To observe the size of the TX pool:
$ cat /sys/kernel/debug/mlx5/<pci>/nic/tls/tx/pool_size

Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Co-developed-by: Gal Pressman <gal@nvidia.com>
Signed-off-by: Gal Pressman <gal@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>