ARM: dove: add gigabit ethernet and mvmdio device tree nodes

This patch adds orion-eth and mvmdio device tree nodes for DT enabled
Dove boards. As there is only one ethernet controller on Dove, a default
phy node is also added with a note to set its reg property on a per-board
basis.

Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>