net: dsa: mv88e6xxx: add IEEE and IP mapping ops

All Marvell switch families except 88E6390 have direct registers in
Global 1 for IEEE and IP priorities override mapping. The 88E6390 uses
indirect tables instead.

Add .ieee_pri_map and .ip_pri_map ops to distinct that and call them
from a mv88e6xxx_pri_setup helper. Only non-6390 are concerned ATM.

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