thermal/x86_pkg_temp: Get rid of ref counting

There is no point in the whole package data refcounting dance because
topology_core_cpumask tells us whether this is the last cpu in the
package. If yes, then the package can go, if not it stays. It's already
serialized via the hotplug code.

While at it rename the first_cpu member of the package structure to
cpu. The first has absolutely no meaning.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>