net: dsa: mv88e6xxx: combine port_set_speed and port_set_duplex

Setting the speed independently of duplex makes little sense; the two
parameters result from negotiation or fixed setup, and may have inter-
dependencies. Moreover, they are always controlled via the same
register - having them split means we have to read-modify-write this
register twice.

Combine the two operations into a single port_set_speed_duplex()
operation. Not only is this more efficient, it reduces the size of the
code as well.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>