powercap/intel_rapl: Add missing domain data update on hotplug

The domain data of packages is only updated at init time, but new packages
created by hotplug miss that treatment.

Add it there and remove the global update at init time, because it's now
obsolete.

The more interesting question is why rapl_update_domain_data() exists at
all as nothing ever uses that data.

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>