hwmon: add MP2891 driver

Add support for MPS VR controller mp2891. This driver exposes
telemetry and limit value readings and writtings.

Signed-off-by: Noah Wang <noahwang.wang@outlook.com>
Link: https://lore.kernel.org/r/SEYPR04MB64828A352836982C0184AA10FAD62@SEYPR04MB6482.apcprd04.prod.outlook.com


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