ARM: mvebu: Add missing MDIO clock in Armada 375

ARM: mvebu: Add missing MDIO clock in Armada 375

In Armada 375 SoCs, the MDIO is handled by a separate orion-mdio driver,
despite the register is contained within the "LMS" block of the network
controller.

Therefore we need to add the clock to the MDIO devicetree to prevent the
controller from being accesed with its clock gated. This is needed, for
instance, to be able to load the MDIO driver before the network driver.

Signed-off-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Link: https://lkml.kernel.org/r/1405961296-5846-7-git-send-email-ezequiel.garcia@free-electrons.com
Signed-off-by: Jason Cooper <jason@lakedaemon.net>