hwmon: (pmbus/ibm-cffps) Add mfg_id debugfs entry

Add support for the manufacturer ID to the debugfs entries.

Signed-off-by: Brandon Wyman <bjwyman@gmail.com>
Link: https://lore.kernel.org/r/20211004144339.2634330-1-bjwyman@gmail.com


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