ARM: mvebu: use the correct phy connection mode on Armada 385 DB

On Armada 385 DB, while the "rgmii" PHY connection mode works fine
with the generic PHY driver, it fails to work when the Marvell PHY
driver is enabled in the kernel configuration, due to a finer handling
of the PHY configuration. This is due to the fact that the phy
connection mode should instead be "rgmii-id", i.e with the TX/RX delay
mechanisms enabled.

This fixes the network operation on Armada 385 DB with
CONFIG_MARVELL_PHY=y. Without this patch and this option enabled, one
would only get messages such as:

  mvneta f1070000.ethernet eth1: bad rx status 0cc10000 (crc error), size=70

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>