hwmon: (ibmpowernv) introduce a legacy_compatibles array

Today, the type of a PowerNV sensor system is determined with the
"compatible" property for legacy Firmwares and with the "sensor-type"
for newer ones. The same array of strings is used for both to do the
matching and this raises some issue to introduce new sensor types.

Let's introduce two different arrays (legacy and current) to make
things easier for new sensor types.

Signed-off-by: Cédric Le Goater <clg@kaod.org>
Tested-by: Shilpasri G Bhat <shilpa.bhat@linux.vnet.ibm.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>