net: dsa: hellcreek: Offload per-tc max SDU from tc-taprio

Add support for configuring the max SDU per priority and per port. If not
specified, keep the default.

Signed-off-by: Kurt Kanzenbach <kurt@linutronix.de>
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>