net: dsa: mv88e6xxx: factorize global setup

Every driver is calling mv88e6xxx_setup_global after
mv88e6xxx_setup_common. Call the former in the latter.

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