hwmon: (pmbus/ibm-cffps) Add new manufacturer debugfs entries

Add support for a number of manufacturer-specific registers in the
debugfs entries, as well as support to read and write the
PMBUS_ON_OFF_CONFIG register through debugfs.

Signed-off-by: Eddie James <eajames@linux.ibm.com>
Link: https://lore.kernel.org/r/1576788607-13567-2-git-send-email-eajames@linux.ibm.com


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