ARM: kirkwood: fix to retain gbe MAC addresses for DT kernels

The ethernet controller used on kirkwood looses its MAC address
register contents when the corresponding clock is gated. As soon as
mv643xx_eth is built as module, the clock gets gated and when loading
the module, the MAC address is gone.

Proper DT support for the mv643xx_eth driver is expected soon, so we add
a workaround to always enable ge0/ge1 clocks on kirkwood. This workaround
is also already used on non-DT kirkwood kernels.

Reported-by: Simon Baatz <gmbnomis@gmail.com>
Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Tested-by: Simon Baatz <gmbnomis@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>