hwmon: (pmbus) Add support for MPS Multi-phase mp5023

Add support for mp5023 device from Monolithic Power Systems, Inc. (MPS)
vendor. This is a Hot-Swap Controller.

Signed-off-by: Howard Chiu <howard.chiu@quantatw.com>
Link: https://lore.kernel.org/r/HKAPR04MB400349AA406694FB976D78D096709@HKAPR04MB4003.apcprd04.prod.outlook.com


[groeck: Added MODULE_IMPORT_NS, entry in index.rst]
Signed-off-by: Guenter Roeck <linux@roeck-us.net>