mfd: ab8500: sysctrl: Initialize driver at arch_initcall

The abx500-clk driver is initiated at arch_initcall level. Moreover it
is relying on the ab8500-sysctrl API to be available. Therefore move
ab8500-sysctrl to arch_initcall level as well. The device is already
added before the abx500 clk device, thus it will be probed before as
well, which is exactly what we want.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>