Implement a very basic multi-PHY aware switch device.

This is intended to be used as a stop-gap for switch devices
which expose multiple ethernet PHYs but we don't have a driver
for - here, etherswitchcfg and the general switch configuration
API can be used to interface to said PHYs.

Submitted by:	Luiz Otavio O Souza <loos.br@gmail.com>