ARM: ux500: Add i2c configurations to the Device Tree for DB8500 based devices

Since initial support was provided for the Nomadik I2C driver, it
has been converted to an AMBA device. AMBA devices are probed in
a slightly different way to other devices, so we have to identify
them using an "arm,primecell" compatible string. As well as doing
just that, this patch specifies which regulators the controller
should use and requests a clock-speed. The latter is provided as
more of an example, as it's the same as the recently changed
default configuration.

Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>