ARM: orion5x: update I2C description at SoC level

This commit fixes the Orion5x SoC definition to:

 * Not define a clock-frequency, as it should be described on a
   per-board basis.

 * Declare the appropriate clock reference, so that the driver can do
   correct divisors calculations for the I2C bus.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Link: https://lkml.kernel.org/r/1398202002-28530-26-git-send-email-thomas.petazzoni@free-electrons.com


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