net: dsa: mv88e6xxx: rework ATU Flush operation

net: dsa: mv88e6xxx: rework ATU Flush operation

These Marvell switches have 4 operations to flush or (re)move, all or
only non-static MAC addresses, from the entire set of databases or from
just a particular one.

The value of the EntryState bits will determine if the operation is
either a Flush (0x0) or a Move (0xF).

When moving entries from one port to another, entries will be removed if
the destination port is 0xF.

This patch renames these operations for consistency, add a new generic
_mv88e6xxx_atu_flush_move function, and change _mv88e6xxx_flush_fid to
use it.

Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: David S. Miller <davem@davemloft.net>