arm: mvebu: Espressobin: move network setup into a separate function

Currently, Esspresobin switch is being setup directly in last_stage_init()
which makes it hard to add support for any other board to be setup.

So, lets just move the switch setup code to a separate function and call it
if compatible matches, there should be no functional change.

Signed-off-by: Robert Marko <robert.marko@sartura.hr>
Reviewed-by: Stefan Roese <sr@denx.de>