net: add Calxeda xgmac driver

This adds ethernet driver for Calxeda xgmac found on Highbank SOC.

Signed-off-by: Rob Herring <rob.herring@calxeda.com>

Fix: WARNING: __aligned(size) is preferred over
__attribute__((aligned(size)))
Signed-off-by: Wolfgang Denk <wd@denx.de>