hwmon: (ibmpowernv) add support for the new device tree

The new OPAL device tree for sensors has a different layout and uses new
property names, for the type and for the handler used to capture the
sensor data.

This patch modifies the ibmpowernv driver to support such a tree in a
way preserving compatibility with older OPAL firmwares.

This is achieved by changing the error path of the routine parsing
an OPAL node name. The node is simply considered being from the new
device tree layout and fallback values are used.

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