hwmon: (pmbus/ibm-cffps) Add the VMON property for version 2

Version 2 of the PSU supports reading an auxiliary voltage. Use the
pmbus VMON property and associated virtual register to read it.

Signed-off-by: Eddie James <eajames@linux.ibm.com>
Link: https://lore.kernel.org/r/1576788607-13567-3-git-send-email-eajames@linux.ibm.com


Signed-off-by: Guenter Roeck <linux@roeck-us.net>