dt-bindings: hwmon: Add MPS mp2891

Add support for MPS mp2891 controller

Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Noah Wang <noahwang.wang@outlook.com>
Link: https://lore.kernel.org/r/SEYPR04MB6482BC95D1242A5675FF9DAEFAD62@SEYPR04MB6482.apcprd04.prod.outlook.com


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