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

Documentation/devicetree/bindings/trivial-devices.yaml

@@ -288,6 +288,8 @@ properties:
           - mps,mp2857
             # Monolithic Power Systems Inc. multi-phase controller mp2888
           - mps,mp2888
+            # Monolithic Power Systems Inc. multi-phase controller mp2891
+          - mps,mp2891
             # Monolithic Power Systems Inc. multi-phase controller mp2971
           - mps,mp2971
             # Monolithic Power Systems Inc. multi-phase controller mp2973