net: dsa: mv88e6xxx: re-order functions

Move mv88e6xxx_setup() below mv88e6xxx_mdios_register(), so that we are
able to call the latter one from here. Do the same thing for the
inverse functions.

Signed-off-by: Klaus Kudielka <klaus.kudielka@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>