PM / domains: Ignore callbacks for subsys generic_pm_domain_data

In a step of simplifying the generic power domain let's move away from
using these callbacks.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Reviewed-by: Kevin Hilman <khilman@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>