ARM: Kirkwood: Enable the second I2C bus

mv64xxx_of_config requires that the tclk frequency be found
through the clk stuff rather than through device tree, so add
another override for the 2nd controller.

Signed-off-by: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>