net: dsa: mv88e6xxx: remove Global 2 setup

The remaining values written to the Switch Management Register in the
mv88e6xxx_g2_setup function are specific to 88E6352 and older, and are
the default values anyway.

Thus remove completely this function. The mv88e6xxx driver no more
contains setup code to access arbitrary Global 2 registers.

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