net: dsa: mt7530: implement port_fast_age

Implement the .port_fast_age DSA operation by flushing all non-static
(dynamically learned) MAC address entries from the address table.

The switch does not offer a combined "non-static AND per-port" match
mode, so the flush is global and the port argument is not used. Unlike
b53 and realtek, which flush the dynamic entries of the affected port
only, an STP topology change on one port therefore also flushes the
dynamically learned entries of the other ports; they are quickly
relearned.

Access the address table control register under priv->reg_mutex, as done
by all other ATC users (FDB and MDB add/del/dump), to serialise the
write-then-poll command sequence, and log a message should the command
fail.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/60f83ade0e371dfe2d974d5d192056935c3ab5c9.1788190568.git.daniel@makrotopia.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>