hwmon: (coretemp) Simplify package management

Keeping track of the per package platform devices requires an extra object,
which is held in a linked list.

The maximum number of packages is known at init() time. So the extra object
and linked list management can be replaced by an array of platform device
pointers in which the per package devices pointers can be stored. Lookup
becomes a simple array lookup instead of a list walk.

The mutex protecting the list can be removed as well because the array is
only accessed from cpu hotplug callbacks which are already serialized.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>