hwmon: (pmbus/max20730) add device monitoring via debugfs

Add debugfs interface support for accessing device specific registers
(MFR_VOUT_MIN, MFR_DEVSET1 and MFR_DEVSET2) and others including
OPERATION, ON_OFF_CONFIG, SMB_ALERT_MASK, VOUT_MODE, VOUT_COMMAND
and VOUT_MAX.
Signed-off-by: Ugur Usug <ugur.usug@maximintegrated.com>
Link: https://lore.kernel.org/r/MWHPR11MB1965C01083AD013C630646B2FD3B0@MWHPR11MB1965.namprd11.prod.outlook.com
[groeck: Resolved conflics seen due to PMBus driver API changes]
Signed-off-by: Guenter Roeck <linux@roeck-us.net>