mlxsw: spectrum: Start using sampling triggers hash table

Start using the previously introduced sampling triggers hash table to
store sampling parameters instead of storing them as attributes of the
sampled port.

This makes it easier to introduce new sampling triggers.

Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>