mlxsw: reg: Add ext and tc-cong counter groups

This adds the counter group definitions for 2 new counter groups
which are necessary for gaining ECN & wred counters.

Signed-off-by: Yuval Mintz <yuvalm@mellanox.com>
Signed-off-by: Nogah Frankel <nogahf@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>