mlxsw: spectrum_qdisc: Support offloading of TBF Qdisc

React to the TC messages that were introduced in a preceding patch and
configure egress maximum shaper as appropriate. TBF can be used as a root
qdisc or under one of PRIO or strict ETS bands.

Signed-off-by: Petr Machata <petrm@mellanox.com>
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>