PM / Domains: Allow to attach a CPU via genpd_dev_pm_attach_by_id|name()

Attaching a device via genpd_dev_pm_attach_by_id|name() makes
genpd allocate a virtual device that it attaches instead. This
leads to a problem in case when the base device belongs to a CPU.
More precisely, it means genpd_get_cpu() compares against the
virtual device, thus it fails to find a matching CPU device.

Address this limitation by passing the base device to genpd_get_cpu()
rather than the virtual device.

Moreover, to deal with detach correctly from genpd_remove_device(),
store the CPU number in struct generic_pm_domain_data, so as to be
able to clear the corresponding bit in the cpumask for the genpd.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>