hwmon: (ibmpowernv) pretty print labels

The new OPAL device tree adds a few properties which can be used to add
extra information on the sensor label.

In the case of a cpu core sensor, the firmware exposes the physical
identifier of the core in the "ibm,pir" property. The driver
translates this identifier in a linux cpu number and prints out a
range corresponding to the hardware threads of the core (as they
share the same sensor).

The numbering gives a hint on the localization of the core in the
system (which socket, which chip).

Signed-off-by: Cédric Le Goater <clg@fr.ibm.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>