net/mlx5: Move TTC logic to fs_ttc

Now that TTC logic is not dependent on mlx5e structs, move it to
lib/fs_ttc.c so it could be used other part of the mlx5 driver.

Signed-off-by: Maor Gottlieb <maorg@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Reviewed-by: Mark Bloch <mbloch@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>