net: mvpp2: support setting hardware addresses from ethernet core

mvpp2 already has support for setting MAC addresses but this
functionality was not exposed to the ethernet core. This commit exposes
this functionality so that MAC address assignments stored in U-Boot's
environment are correctly applied before Linux boots.

Signed-off-by: Matt Pelland <mpelland@starry.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>