powercap/intel_rapl: Cleanup duplicated init code

The whole init/exit code is a duplicate of the cpuhotplug code. So we can
just let the hotplug code do the actual work of setting up and tearing down
the domains.

This also restores the package hardware when a package is removed during
hotplug instead of leaving it in the last configured state and only reset
it when the driver is removed.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>