arm: kirkwood: GoFlex Home: Use Ethernet PHY name and address from device tree

In DM Ethernet, the old "egiga0" name is no longer valid,
so replace these with Ethernet PHY names from device tree. Also, read
Ethernet PHY address from device tree.

Signed-off-by: Tony Dinh <mibodhi@gmail.com>
Reviewed-by: Stefan Roese <sr@denx.de>