net: mv643xx_eth: add DT parsing support

This adds device tree parsing support for the shared driver of mv643xx_eth.
As the bindings are slightly different from current PPC bindings new binding
documentation is also added. Following PPC-style device setup, the shared
driver now also adds port platform_devices and sets up port platform_data.

Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>