The abx500 clock driver is a platform driver which will be initialized
during arch init. The platform device shall be added from the ab-core
driver as a mfd child device to maintain correct boot sequence.

Depending on what ab version we use, different clock definitions will
be added.
Signed-off-by: NUlf Hansson <ulf.hansson@linaro.org>
Reviewed-by: NLinus Walleij <linus.walleij@linaro.org>
Signed-off-by: NMike Turquette <mturquette@linaro.org>