ARM: integrator: switch to fetch clocks from device tree

This atomic commit changes the Integrator clock implementation
and the machines to register clocks from the device tree and
use these instead of the previous hard-coded clocks.

In the clock implementation all hard-coded clocks and the
special initialization function call goes away, and is
replaced by two compatible strings for the two clocks
available on the core module.

Cc: Mike Turquette <mturquette@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>